Mix Examples - Acids, Bases and Salts Questions in English

(N/A) The gas that extinguishes a burning candle is carbon dioxide $(CO_2)$. Since the reaction produces $CO_2$ and calcium chloride $(CaCl_2)$ from a metal compound $A$ and hydrochloric acid $(HCl)$,the metal compound $A$ must be calcium carbonate $(CaCO_3)$.
The balanced chemical equation is:
$CaCO_{3(s)} + 2HCl_{(aq)} \rightarrow CaCl_{2(aq)} + CO_{2(g)} + H_2O_{(l)}$

(A) According to the law of stoichiometry,the neutralization reaction between $NaOH$ and $HCl$ occurs in a fixed ratio.
Given that $10 \,mL$ of $NaOH$ requires $8 \,mL$ of $HCl$ for complete neutralization.
If the volume of $NaOH$ is doubled to $20 \,mL$,the amount of $HCl$ required will also be doubled proportionally.
Calculation: $(20 \,mL \,NaOH / 10 \,mL \,NaOH) \times 8 \,mL \,HCl = 2 \times 8 \,mL = 16 \,mL$.
Therefore,$16 \,mL$ of $HCl$ solution is required.

(C) Step $1$: Distilled water is a pure form of water and is devoid of any dissolved ionic species. Since electrical conduction requires the movement of free ions, distilled water does not conduct electricity.
Step $2$: Rain water, while falling through the atmosphere, dissolves atmospheric gases like $CO_2$ and $SO_2$ to form acids such as carbonic acid and sulfuric acid.
Step $3$: These acids dissociate into ions in the water. The presence of these free ions allows rain water to conduct electricity.

(N/A) The milkman shifts the $pH$ of the fresh milk from $6$ to slightly alkaline to prevent the milk from turning sour quickly. In an alkaline condition,the growth of lactic acid-producing bacteria is inhibited,which prevents the milk from spoiling.
$(b)$ Since this milk is slightly basic,the lactic acid produced by bacteria during the fermentation process is neutralized by the added baking soda. Therefore,it takes a longer time for the milk to reach the required acidity level to set as curd.

(N/A) $1$. Place a drop of each solution on the red litmus paper. The solution that turns the red litmus paper blue is the basic solution.
$2$. Now,we have two test tubes left: one containing distilled water (neutral) and the other containing an acidic solution.
$3$. Take the identified basic solution and mix a drop of it with a drop of each of the two remaining unknown solutions separately.
$4$. Test these mixtures with the red litmus paper. The mixture that turns the red litmus paper blue indicates that the added solution was neutral (distilled water),as the basic property remains dominant.
$5$. The mixture that does not change the colour of the red litmus paper indicates that the added solution was acidic,as the acid neutralized the base.

(A) $1$. When $NaOH$ and anhydrous $CuSO_4$ are dissolved in water,the temperature of the solution increases. This indicates that heat is released during the dissolution process,which is characteristic of an exothermic process.
$2$. When $NaCl$ is dissolved in water,the temperature of the solution decreases. This indicates that heat is absorbed from the surroundings,which is characteristic of an endothermic process.
$3$. Therefore,statement $(i)$ is correct because beakers $A$ and $B$ involve exothermic processes.
$4$. Statement $(iv)$ is correct because beaker $C$ involves an endothermic process.
$5$. Thus,the correct combination is $(i)$ and $(iv)$.

(A) When an acid reacts with a base,a neutralization reaction occurs.
This reaction is exothermic in nature,meaning it releases heat energy into the surroundings,which causes the temperature of the solution to increase.
As a result of the neutralization reaction,salt and water are produced $(Acid + Base \rightarrow Salt + Water)$.
Therefore,both statement $(i)$ (temperature increases) and statement $(iv)$ (salt formation takes place) are correct.

(B) solution that turns red litmus blue is basic in nature.
To reverse this change, we need to neutralize the base by adding an acid.
Among the given options, $Hydrochloric acid$ $(HCl)$ is a strong acid.
Adding an excess of $HCl$ will neutralize the basic solution and turn the blue litmus back to red.

(C) The pH paper turning yellowish-orange indicates that the soil solution is acidic (pH < $7$).
To change the colour of the pH paper to greenish-blue,we need to add a substance that is basic (alkaline) in nature (pH > $7$).
$A$. Lemon juice is acidic.
$B$. Vinegar is acidic.
$C$. An antacid is basic (alkaline) and neutralizes the acid,shifting the pH towards the basic range (greenish-blue).
$D$. Common salt is neutral.

(A) When a concentrated acid spills on the skin,the immediate priority is to dilute and remove the acid to prevent further tissue damage.
$1$. Wash the affected area immediately with plenty of running water to dilute the acid.
$2$. After washing,apply a mild base like sodium hydrogencarbonate $(NaHCO_3)$ paste. This helps to neutralize any remaining traces of acid on the skin.
$3$. Using a strong alkali (like $NaOH$) is dangerous because it can cause severe chemical burns itself.
Therefore,the correct action is to wash with water and apply a mild base like sodium hydrogencarbonate.

(B) When sodium hydrogencarbonate $(NaHCO_3)$ reacts with acetic acid $(CH_3COOH)$,it produces sodium acetate,water,and carbon dioxide $(CO_2)$ gas.
The chemical reaction is: $CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2$.
Properties of $CO_2$ gas:
$(i)$ It turns lime water milky due to the formation of calcium carbonate $(CaCO_3)$. This is a true statement.
$(ii)$ It does not support combustion,so it extinguishes a burning splinter. This is a true statement.
$(iii)$ It is an acidic oxide and reacts with sodium hydroxide $(NaOH)$ to form sodium carbonate and water. This is a true statement.
$(iv)$ $CO_2$ is an odourless gas,so it does not have a pungent odour. This is a false statement.
Therefore,statements $(i)$,$(ii)$,and $(iii)$ are correct.

(D) When a small amount of acid is added to water, the following processes occur:
$1$. Ionisation: The acid molecules dissociate into their respective ions (e.g., $HCl + H_2O \rightarrow H_3O^+ + Cl^-$). This is the process of ionisation.
$2$. Dilution: Adding a small amount of acid to a large volume of water decreases the concentration of $H_3O^+$ ions per unit volume, which is known as dilution.
Therefore, both ionisation and dilution occur. The correct option is $(D)$.

(B) Marble $(CaCO_3)$,Baking soda $(NaHCO_3)$,and Limestone $(CaCO_3)$ are carbonates or bicarbonates. When these react with dilute acids,they release carbon dioxide $(CO_2)$ gas.
For example: $CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2 \uparrow$.
Lime $(CaO)$,also known as quicklime,is a metal oxide. When it reacts with dilute acid,it undergoes a neutralization reaction to form salt and water,but it does not release carbon dioxide gas.
Reaction: $CaO + 2HCl \rightarrow CaCl_2 + H_2O$.

(D) $1$. Metal carbonates react with acids to produce salt,water,and $CO_2$ gas. This is a correct statement.
$2$. Non-metal oxides (like $SO_2$,$CO_2$) are acidic in nature and react with water to form acids (like $H_2SO_3$,$H_2CO_3$). This is a correct statement.
$3$. Many reactive metals (like $Zn$,$Fe$) react with dilute acids to produce salt and hydrogen gas. This is a correct statement.
$4$. Metal oxides are generally basic in nature. While some (like alkali metal oxides) react with water to form bases (alkalis),they do not react with water to form salt and acid. Therefore,this statement is incorrect.

$(A)$ The correct matches are as follows:
$1$. Bleaching powder $(CaOCl_2)$ is used for decolourisation (bleaching action) in the textile and paper industries. Thus, $(A)-(iii)$.
$2$. Baking soda $(NaHCO_3)$ is used as an antacid to neutralize excess stomach acid. Thus, $(B)-(iv)$.
$3$. Washing soda $(Na_2CO_3 \cdot 10H_2O)$ is used in the glass, soap, and paper industries. Thus, $(C)-(i)$.
$4$. Sodium chloride $(NaCl)$ is used in the chlor-alkali process for the production of $H_2$ and $Cl_2$ gases. Thus, $(D)-(ii)$.
Therefore, the correct sequence is $A-(iii), B-(iv), C-(i), D-(ii)$.

(N/A) The action of these substances on litmus paper depends on their acidic or basic nature. Acids turn blue litmus red,while bases turn red litmus blue. Dry $HCl$ gas does not show acidic properties because it lacks $H^+$ ions in the absence of water. Moistened $NH_3$ gas acts as a base $(NH_4OH)$. Lemon juice,carbonated soft drinks,and curd are acidic. Soap solution is basic.

Substance	Action on Litmus paper
Dry $HCl$ gas	No change
Moistened $NH_3$ gas	Turns red to blue
Lemon juice	Turns blue to red
Carbonated soft drink	Turns blue to red
Curd	Turns blue to red
Soap solution	Turns red to blue

(B) Egg shells are primarily composed of calcium carbonate $(CaCO_3)$.
When nitric acid $(HNO_3)$ is added to the egg shell,a chemical reaction occurs between the acid and the carbonate.
This reaction results in the evolution of carbon dioxide $(CO_2)$ gas,along with the formation of calcium nitrate and water.
The balanced chemical equation for this reaction is:
$CaCO_3 + 2HNO_3 \rightarrow Ca(NO_3)_2 + H_2O + CO_2 \uparrow$

(B) Since both solutions are colourless and litmus paper is unavailable,the student can use other indicators.
$1$. Phenolphthalein: It turns pink in a basic solution and remains colourless in an acidic solution.
$2$. Natural indicators: Turmeric turns reddish-brown in a base and remains yellow in an acid. China rose (Hibiscus) solution turns dark pink (magenta) in an acid and green in a base.

(N/A) The chemical formula of baking powder is sodium hydrogencarbonate $(NaHCO_3)$,while the chemical formula of washing soda is sodium carbonate decahydrate $(Na_2CO_3 \cdot 10H_2O)$.
When baking powder $(NaHCO_3)$ is heated,it undergoes thermal decomposition to release carbon dioxide $(CO_2)$ gas. This gas turns lime water milky.
$2NaHCO_3 \xrightarrow{\text{Heat}} Na_2CO_3 + H_2O + CO_2 \uparrow$
In contrast,washing soda $(Na_2CO_3 \cdot 10H_2O)$ loses its water of crystallization upon heating but does not release $CO_2$ gas. Therefore,it does not turn lime water milky.
$Na_2CO_3 \cdot 10H_2O \xrightarrow{\text{Heat}} Na_2CO_3 + 10H_2O$

(N/A) Hydrogen gas will evolve with greater speed because zinc dust has a larger surface area compared to zinc granules,which increases the rate of reaction.
$(b)$ Almost the same amount of hydrogen gas will be evolved as both are strong mineral acids.
$(c)$ Hydrogen gas will not be evolved because copper is less reactive than hydrogen and cannot displace it from the acid.
$(d)$ If sodium hydroxide is taken,hydrogen gas will be evolved upon heating:
$Zn + 2NaOH \to Na_2ZnO_2 + H_2$ (Sodium zincate is formed along with hydrogen gas).

(X=CACO3, Y=CA(OH)2, G=CL2, Z=CAOCL2) $1$. The gas evolved at the anode during the electrolysis of brine ($NaCl$ solution) is chlorine gas $(G = Cl_2)$.
$2$. When chlorine gas is passed over dry slaked lime $(Y = Ca(OH)_2)$,it produces bleaching powder $(Z = CaOCl_2)$,which is used for disinfecting drinking water.
$3$. The reaction is: $Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O$.
$4$. Since $Y$ is calcium hydroxide,the metal carbonate $X$ is calcium carbonate $(CaCO_3)$.
$5$. When $CaCO_3$ reacts with an acid (e.g.,$HCl$),it releases $CO_2$ gas: $CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2$.
$6$. When this $CO_2$ is passed through lime water $(Ca(OH)_2)$,it turns milky due to the formation of $CaCO_3$: $Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O$.

(N/A) The common base $B$ is Sodium hydroxide $(NaOH)$. It is a deliquescent substance,meaning it absorbs moisture from the atmosphere and becomes sticky.
The reaction between a base and an acidic oxide is a neutralization reaction,which produces salt and water.
When $NaOH$ reacts with carbon dioxide $(CO_2)$,which is an acidic oxide,the balanced chemical equation is:
$2NaOH + CO_2 \rightarrow Na_2CO_3 + H_2O$

(N/A) Based on the given reactions:
$1$. $X + Zn \rightarrow A + H_2(g)$: $A$ base reacts with zinc to produce hydrogen gas. Thus,$X$ is a base,$NaOH$.
$2$. $X + HCl \rightarrow B + H_2O$: $A$ base reacts with an acid to form salt and water (neutralization). Thus,$B$ is $NaCl$.
$3$. $X + CH_3COOH \rightarrow C + H_2O$: $A$ base reacts with acetic acid to form salt and water. Thus,$C$ is $CH_3COONa$.
Final identifications:
$X = NaOH$ (Sodium hydroxide)
$A = Na_2ZnO_2$ (Sodium zincate)
$B = NaCl$ (Sodium chloride)
$C = CH_3COONa$ (Sodium acetate)

(B) Acid rain is primarily caused by the emission of acidic oxides such as sulphur dioxide $(SO_2)$,nitrogen oxides $(NO_x)$,and carbon dioxide $(CO_2)$ into the atmosphere.
These gases are released mainly through the burning of fossil fuels,industrial processes,and vehicular emissions.
When these gases react with water vapor in the atmosphere,they form acids like sulphuric acid $(H_2SO_4)$,nitric acid $(HNO_3)$,and carbonic acid $(H_2CO_3)$.
These acids then dissolve in rainwater,lowering its $pH$ and resulting in acid rain.

(N/A) When dilute $HCl$ reacts with sodium hydrogen carbonate $(NaHCO_3)$,the gas evolved is carbon dioxide $(CO_2)$.
The chemical reaction is: $NaHCO_3 + HCl \rightarrow NaCl + H_2O + CO_2 \uparrow$.
This gas is recognized by passing it through lime water $(Ca(OH)_2)$. It turns the lime water milky due to the formation of insoluble calcium carbonate $(CaCO_3)$.

(D) $HCl$ is a strong acid because it undergoes complete dissociation in an aqueous solution,releasing a high concentration of $H^+$ ions.
In contrast,acetic acid is a weak acid that undergoes only partial dissociation in water,resulting in a lower concentration of $H^+$ ions for the same molar concentration.
Therefore,due to the higher degree of ionization,$HCl$ exhibits stronger acidic properties.

(N/A) Calcium carbonate reacts with hydrochloric acid to form calcium chloride,water,and carbon dioxide:
$CaCO_{3} + 2HCl \rightarrow CaCl_{2} + H_{2}O + CO_{2}$
$(b)$ Calcium oxychloride (bleaching powder) reacts with hydrochloric acid to form calcium chloride,water,and chlorine gas:
$CaOCl_{2} + 2HCl \rightarrow CaCl_{2} + H_{2}O + Cl_{2}$
$(c)$ Sodium hydroxide reacts with zinc to form sodium zincate and hydrogen gas:
$2NaOH + Zn \rightarrow Na_{2}ZnO_{2} + H_{2}$

(N/A) The given reactions are neutralization reactions where an acid reacts with a base to form salt and water.
$(i)$ $HNO_{3} + NaOH \rightarrow NaNO_{3} + H_{2}O$. Here,$A$ is $NaNO_{3}$ (Sodium nitrate).
$(ii)$ $H_{2}SO_{4} + Ca(OH)_{2} \rightarrow CaSO_{4} + 2H_{2}O$. Here,$B$ is $H_{2}SO_{4}$ (Sulphuric acid).
$(iii)$ $HCl + KOH \rightarrow KCl + H_{2}O$. Here,$C$ is $KOH$ (Potassium hydroxide).

(D) $(i)$ Between hydrochloric acid and acetic acid of the same concentration,acetic acid will produce a lower concentration of $H^{+}$ ions because it is a weak acid that does not ionize completely in water.
$(ii)$ Acetic acid is the weak acid.
$(b)$ If someone is suffering from acidity,$I$ would suggest a baking soda solution to cure it. Baking soda is a mild base (sodium bicarbonate) that neutralizes the excess hydrochloric acid produced in the stomach,thereby providing relief.

(N/A) $(i)$ Antacids are formulated based on the principle of neutralisation reaction to treat acidity.
$(ii)$ Toothpastes are basic in nature,which help in neutralising the excess acid produced in the mouth,thereby preventing tooth decay.
$(iii)$ Milkmen add a small amount of baking soda to milk to neutralise the lactic acid produced,which helps in preventing the milk from souring quickly.

(N/A) The salt formed by the reaction of carbonic acid $(H_{2}CO_{3})$ and sodium hydroxide $(NaOH)$ is sodium carbonate,with the formula $Na_{2}CO_{3}$.
$(b)$ The chlor-alkali process involves the electrolysis of brine $(NaCl$ solution$)$,which produces sodium hydroxide $(NaOH)$,chlorine gas,and hydrogen gas. The basic substance formed is sodium hydroxide $(NaOH)$.
$(c)$ Sodium hydrogen carbonate $(NaHCO_{3})$,also known as baking soda,is added to cakes. Upon heating,it releases carbon dioxide gas,which makes the cakes fluffy.

(N/A) $(i)$ The reaction of zinc metal with dilute hydrochloric acid produces zinc chloride and hydrogen gas: $Zn(s) + 2HCl(aq) \rightarrow ZnCl_{2}(aq) + H_{2}(g)$.
$(ii)$ The reaction of sodium carbonate with dilute hydrochloric acid produces sodium chloride,water,and carbon dioxide gas: $Na_{2}CO_{3}(s) + 2HCl(aq) \rightarrow 2NaCl(aq) + H_{2}O(l) + CO_{2}(g)$.
$(iii)$ The reaction of sodium hydroxide (a base) with dilute hydrochloric acid (an acid) is a neutralization reaction producing sodium chloride and water: $NaOH(aq) + HCl(aq) \rightarrow NaCl(aq) + H_{2}O(l)$.

(N/A) $Ca(OH)_{2} + Cl_{2} \longrightarrow CaOCl_{2} + H_{2}O$ (Bleaching powder is formed).
$(b)$ $CaSO_{4} \cdot 1/2 H_{2}O + 1 \frac{1}{2} H_{2}O \longrightarrow CaSO_{4} \cdot 2H_{2}O$ (Gypsum is formed).
$(c)$ $Na_{2}CO_{3} \cdot 10H_{2}O \xrightarrow{\text{air}} Na_{2}CO_{3} \cdot H_{2}O + 9H_{2}O$ (Efflorescence occurs,forming sodium carbonate monohydrate).

(N/A) Copper sulphate pentahydrate $(CuSO_4 \cdot 5H_2O)$ crystals are blue due to the presence of $5$ molecules of water of crystallisation. On heating, they lose these water molecules and become anhydrous copper sulphate $(CuSO_4)$, which is white in colour.
$(b)$ Baking soda $(NaHCO_3)$ is mildly alkaline in nature. When taken, it reacts with the excess hydrochloric acid $(HCl)$ produced in the stomach, neutralising it and providing relief from acidity.
$(c)$ The process of diluting a concentrated acid is highly exothermic. If water is added to a concentrated acid, the large amount of heat generated can cause the mixture to splash out, potentially causing severe acid burns. Therefore, acid is always added to water slowly with constant stirring.

(N/A) The colour of the solution becomes blue-green and the copper oxide dissolves. The chemical reaction is: $CuO + 2HCl \rightarrow CuCl_2 + H_2O$.
$(b)$ Aqueous solution of $HCl$ dissociates to produce $H^+$ ions,which are responsible for its acidic character. However,glucose $(C_6H_{12}O_6)$ is a covalent compound that does not dissociate into ions in water; therefore,it does not produce $H^+$ ions and fails to show acidic character.

(N/A) When chlorine is passed over dry slaked lime $(Ca(OH)_2)$,it forms bleaching powder $(CaOCl_2)$ and water $(H_2O)$. The balanced equation is: $Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O$
$(b)$ When sodium bicarbonate $(NaHCO_3)$ reacts with dilute hydrochloric acid $(HCl)$,it produces sodium chloride $(NaCl)$,water $(H_2O)$,and carbon dioxide $(CO_2)$. The balanced equation is: $NaHCO_3 + HCl \rightarrow NaCl + H_2O + CO_2$
$(c)$ When sodium bicarbonate $(NaHCO_3)$ is heated,it undergoes thermal decomposition to form sodium carbonate $(Na_2CO_3)$,water $(H_2O)$,and carbon dioxide $(CO_2)$. The balanced equation is: $2NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + H_2O + CO_2$

(N/A) universal indicator is a mixture of several indicators that exhibits different colours at different concentrations of hydrogen ions in a solution,allowing for the determination of the $pH$ value.
$(b)$ The process is known as the Chlor-alkali process. The chemical equation is: $2NaCl(aq) + 2H_2O(l) \rightarrow 2NaOH(aq) + Cl_2(g) + H_2(g)$.

(A) Vigorous reaction will be seen in test tube $A$.
$(b)$ This is because $H_{2}SO_{4}$ is a strong acid,whereas $H_{2}CO_{3}$ is a weak acid.
$(c)$ $(i)$ Hydrogen gas $(H_{2})$ is liberated in both test tubes.
$(ii)$ When a burning candle is brought near the evolving gas,it burns with a 'pop' sound. This confirms the presence of hydrogen gas.

(B) The chemical equations for the reactions are:
$Mg(s) + H_{2}SO_{4}(aq) \rightarrow MgSO_{4}(aq) + H_{2}(g)$
$Mg(s) + H_{2}CO_{3}(aq) \rightarrow MgCO_{3}(s) + H_{2}(g)$
$(b)$ $H_{2}SO_{4}$ is a strong acid,while $H_{2}CO_{3}$ is a weak acid.
Therefore,$H_{2}SO_{4}$ will have a lower $pH$ value because it dissociates completely to provide a higher concentration of $H^{+}$ ions.
Conversely,$H_{2}CO_{3}$ will have a lower $H^{+}$ concentration because it is a weak acid and dissociates only partially.

(N/A) The common salt used in food is sodium chloride $(NaCl)$. It is formed by the combination of hydrochloric acid $(HCl)$ and sodium hydroxide $(NaOH)$. The primary source of common salt is seawater (ocean water).
$(b)$ Rock salt refers to large deposits of solid salt found in several parts of the world. It is often brown in colour due to the presence of impurities.
$(c)$ When electricity is passed through an aqueous solution of sodium chloride (brine),it decomposes to form sodium hydroxide,chlorine gas,and hydrogen gas. This process is known as the chlor-alkali process. The chemical equation is: $2NaCl(aq) + 2H_2O(l) \xrightarrow{\text{Electricity}} 2NaOH(aq) + Cl_2(g) + H_2(g)$.

(N/A) Tooth decay starts when the $pH$ of the mouth falls below $5.5$. This occurs when bacteria present in the mouth produce acids by degrading sugar and food particles remaining in the mouth after eating. Using toothpaste,which is generally basic,helps neutralize the excess acid and prevents tooth decay.
$(b)$ If the $pH$ of a salt solution is greater than $7$,the nature of the salt is basic.
$(i)$ For Potassium sulphate $(K_2SO_4)$: Base is $KOH$ (Potassium hydroxide) and Acid is $H_2SO_4$ (Sulphuric acid).
$(ii)$ For Ammonium chloride $(NH_4Cl)$: Base is $NH_4OH$ (Ammonium hydroxide) and Acid is $HCl$ (Hydrochloric acid).

(N/A) An aqueous solution of sodium chloride $(NaCl)$ is neutral because it is a salt formed from the neutralization reaction between a strong acid $(HCl)$ and a strong base $(NaOH)$. Since both components are strong,the resulting salt solution does not undergo hydrolysis to change the $pH$ of the water,remaining at $pH = 7$.
An aqueous solution of sodium $(Na)$ is basic because sodium is a highly reactive alkali metal. When it reacts with water,it produces sodium hydroxide $(NaOH)$,which is a strong base,and hydrogen gas $(H_2)$. The presence of $NaOH$ in the solution increases the concentration of hydroxide ions $(OH^-)$,making the solution basic.
The chemical reaction is: $2Na(s) + 2H_2O(l) \longrightarrow 2NaOH(aq) + H_2(g)$

(N/A) Strong electrolytes are substances that dissociate completely into ions when dissolved in an aqueous solution. They conduct electricity very well due to the high concentration of ions. Examples: $NaCl$ (Sodium chloride) and $HCl$ (Hydrochloric acid).
Weak electrolytes are substances that dissociate only partially into ions in an aqueous solution. They conduct electricity poorly because only a small fraction of the molecules exist as ions. Examples: $CH_{3}COOH$ (Acetic acid) and $NH_{4}OH$ (Ammonium hydroxide).

(N/A) Dilute hydrochloric acid reacts with magnesium to form magnesium chloride and hydrogen gas is liberated.
$Mg(s) + 2HCl(aq) \longrightarrow MgCl_2(aq) + H_2(g)$
$(b)$ The reaction between dilute hydrochloric acid and sodium hydroxide is a neutralization reaction,forming sodium chloride salt and water.
$NaOH(aq) + HCl(aq) \longrightarrow NaCl(aq) + H_2O(l)$
$(c)$ Egg shells are primarily composed of calcium carbonate $(CaCO_3)$. Dilute hydrochloric acid reacts with calcium carbonate to produce calcium chloride,carbon dioxide gas,and water.
$CaCO_3(s) + 2HCl(aq) \longrightarrow CaCl_2(aq) + CO_2(g) + H_2O(l)$

(N/A) $(i)$ The process of diluting a concentrated acid is a highly exothermic reaction. If water is added to a concentrated acid,the large amount of heat generated can cause the mixture to splash out,potentially leading to severe acid burns.
$(ii)$ Compounds like alcohol and glucose contain hydrogen,but they do not dissociate to release hydrogen ions $(H^+)$ when dissolved in water. Since acidic behavior is defined by the presence of $H^+$ ions in an aqueous solution,these compounds do not exhibit acidic properties.

(N/A) $(i)$ Plaster of Paris is written as $CaSO_{4} \cdot 1/2 H_{2}O$ because two formula units of $CaSO_{4}$ share one molecule of water of crystallization. This means that one water molecule is associated with two $CaSO_{4}$ units,effectively resulting in $1/2 H_{2}O$ per unit.
$(ii)$ Sodium hydrogen carbonate $(NaHCO_{3})$ is a mild,non-corrosive basic salt. It acts as an antacid by neutralizing the excess hydrochloric acid $(HCl)$ produced in the stomach,thereby providing relief from acidity.
$(iii)$ The electrolysis of an aqueous solution of sodium chloride (brine) produces chlorine gas $(Cl_{2})$ at the anode and sodium hydroxide $(NaOH)$,which is an alkali,at the cathode. Due to the formation of these two specific products,the process is termed the chlor-alkali process.

(A) When an acid reacts with a base,a neutralization reaction occurs.
This reaction is exothermic in nature,meaning heat is released,which causes the temperature of the solution to increase.
The products formed in this reaction are salt and water.
Therefore,both statement $(i)$ (temperature increases) and statement $(iv)$ (salt formation takes place) are correct.

(B) The $pH$ range of $3.5-4.5$ indicates that the river water is highly acidic.
Lead battery manufacturing factories typically use sulfuric acid $(H_2SO_4)$ in their production processes.
If the effluents from these factories are discharged into the river without proper treatment,the sulfuric acid significantly lowers the $pH$ of the water,making it acidic.
Soap and detergent factories often release alkaline substances,while plastic and alcohol industries do not typically release strong mineral acids as their primary effluent that would cause such a drastic drop in $pH$.

(D) An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent,such as water.
When an electric potential is applied across an electrolyte,the dissolved solute dissociates into charged particles called ions.
The positive ions (cations) move towards the cathode (negative electrode),and the negative ions (anions) move towards the anode (positive electrode).
Therefore,the flow of electric current through an electrolyte is due to the movement of both positive and negative ions.

(D) Molarity $(M)$ is defined as the number of moles of solute dissolved per liter of solution.
Formula: $M = \frac{\text{moles of solute}}{\text{volume of solution in liters}}$
Given:
Moles of solute $(HCl)$ = $2 \ mol$
Volume of solution = $500 \ ml = 0.5 \ L$
Calculation:
$M = \frac{2 \ mol}{0.5 \ L} = 4 \ M$
Therefore,the molarity of the solution is $4 \ M$.