What is the percentage of $H_{2}SO_{4}$ in concentrated $H_{2}SO_{4}$ (in $\%$)?

$(a)$ What is a universal indicator?
$(b)$ Write the chemical equation involved in the preparation of sodium hydroxide. Name the process.

Three beakers labelled as $A$,$B$ and $C$ each containing $25 \, mL$ of water were taken. $A$ small amount of $NaOH$,anhydrous $CuSO_4$ and $NaCl$ were added to the beakers $A$,$B$ and $C$ respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers $A$ and $B$,whereas in case of beaker $C$,the temperature of the solution falls. Which one of the following statement$(s)$ is(are) correct?
$(i)$ In beakers $A$ and $B$,exothermic process has occurred.
$(ii)$ In beakers $A$ and $B$,endothermic process has occurred.
$(iii)$ In beaker $C$ exothermic process has occurred.
$(iv)$ In beaker $C$ endothermic process has occurred.

Metal compound $A$ reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

What is the percentage of $H_{2}SO_{4}$ in dilute sulfuric acid (in $\%$)?

Name the gas evolved when dilute $HCl$ reacts with sodium hydrogen carbonate. How is it recognized?