Which of the following is a compound of hydrogen and oxygen?

Which of the following cannot be used as an antacid for the treatment of acidity?

$A$ milkman adds a very small amount of baking soda to fresh milk.
$(a)$ Why does he shift the $pH$ of the fresh milk from $6$ to slightly alkaline?
$(b)$ Why does this milk take a long time to set as curd?

What happens when nitric acid is added to an egg shell?

$A$ metal carbonate $X$ on reacting with an acid gives a gas which when passed through a solution $Y$ gives the carbonate back. On the other hand,a gas $G$ that is obtained at anode during electrolysis of brine is passed on dry $Y$,it gives a compound $Z$,used for disinfecting drinking water. Identify $X$,$Y$,$G$ and $Z$.

$10 \,mL$ of a solution of $NaOH$ is found to be completely neutralized by $8 \,mL$ of a given solution of $HCl$. If we take $20 \,mL$ of the same solution of $NaOH$,the amount of $HCl$ solution (the same solution as before) required to neutralize it will be ...... $mL$.