When a standard solution of $NaOH$ is left in air for a few hours,

Fill in the blanks given below:
$(i)$ The mass of $1$ mole of a substance expressed in grams is called its .........
$(ii)$ The amount of solute dissolved in $1$ $kg$ of solvent is called its .........
$(iii)$ The Fahrenheit scale in a thermometer is marked between .........
$(iv)$ In $NaCl$,each $Na^{+}$ ion is surrounded by ......... $Cl^{-}$ ions.

$A$ mixture of hydrogen and oxygen contains $20\%$ by weight of hydrogen. Find the total number of molecules per gram of the mixture.

Iron sulphide is heated in air to form $A$, an oxide of sulphur. $A$ is dissolved in water to give an acid. The basicity of this acid is:

The volume of $HCl$,containing $73 \ g \ L^{-1}$,required to completely neutralize $NaOH$ obtained by reacting $0.69 \ g$ of metallic sodium with water,is $........ mL$. (Nearest Integer) (Given: molar masses of $Na, Cl, O, H$ are $23, 35.5, 16$ and $1 \ g \ mol^{-1}$ respectively)

An aqueous solution of $6.3 \ g$ oxalic acid dihydrate is made up to $250 \ mL$. The volume of $0.1 \ N \ NaOH$ required to completely neutralize $10 \ mL$ of this solution is $...... \ mL$.