The two major constituents of Portland cement are

Match the following columns:

Column-$I$	Column-$II$
$(i)$ Solvay process	$(p)$ $Na_2O$
$(ii)$ Evolve $CO_2$ on heating	$(q)$ $Na_2O_2$
$(iii)$ Aqueous solution is not neutral towards litmus	$(r)$ $NaHCO_3$
$(iv)$ Used as air purifier in submarine	$(s)$ $Na_2CO_3$

Match the following substances in List-$I$ with their uses in List-$II$:
| List-$I$ (Substance) | List-$II$ (Use) |
| :--- | :--- |
| $(A)$ $Na_2O_2$ | $(I)$ Photoelectric cells |
| $(B)$ $D_2O$ | $(II)$ Antacid |
| $(C)$ $Cs$ | $(III)$ Oxidising agent |
| $(D)$ $Mg(OH)_2$ | $(IV)$ Moderator |

An aqueous solution of a colourless metal sulphate $M$ gives a white precipitate with $NaOH$. This precipitate is soluble in excess of $NaOH$. On passing $H_2S$ through this solution,a white precipitate is formed. The metal $M$ in the salt is:

Which of the following is the main component of Portland cement (besides lime)?

Which of the following is an $\text{Incorrect}$ statement?