What is the molecular mass of $NaOH$?

Write balanced chemical equations for the reaction of dilute $HCl$ with:
$(i)$ $Zn$ metal.
$(ii)$ $Na_{2}CO_{3}$.
$(iii)$ $NaOH$.

What will be the action of the following substances on litmus paper? Dry $HCl$ gas,Moistened $NH_3$ gas,Lemon juice,Carbonated soft drink,Curd,Soap solution.

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

What is the number of moles of solute dissolved in $1 \ L$ of solution called?

In the following schematic diagram for the preparation of hydrogen gas as shown in the Figure,what would happen if the following changes are made?
$(a)$ In place of zinc granules,the same amount of zinc dust is taken in the test tube.
$(b)$ Instead of dilute sulphuric acid,dilute hydrochloric acid is taken.
$(c)$ In place of zinc,copper turnings are taken.
$(d)$ Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.