The number of chlorine atoms in $20 \, mL$ of chlorine gas at $STP$ is ..... $\times 10^{21}$. (Round off to the Nearest Integer).
[Assume chlorine is an ideal gas at $STP$,$R = 0.083 \, L \, bar \, mol^{-1} \, K^{-1}$,$N_{A} = 6.023 \times 10^{23}$]

Phosphoric acid $(H_3PO_4)$ is a tribasic acid,and one of its salts is sodium dihydrogen phosphate $(NaH_2PO_4)$. What volume of $1 \, M \, NaOH$ solution (in $mL$) must be added to $12 \, g$ of sodium dihydrogen phosphate (molar mass $= 120 \, g/mol$) to convert it into trisodium phosphate $(Na_3PO_4)$?

While combusting in air, $4 \ g$ of $H_2$ gas was completely converted into water. If $36 \ \mu mole$ of $CO_2$ from air is dissolved into that water, what is the concentration of $CO_2$?

What is the volume occupied by $32 \ g$ methane gas at $STP$ (in $dm^3$)?

The amount of $Na_2S_2O_3 \cdot 5H_2O$ required to completely reduce $100 \, mL$ of $0.25 \, N$ iodine solution is $.... \, g$.

Combustion of glucose $(C_6H_{12}O_6)$ produces $CO_2$ and water. The amount of oxygen (in $g$) required for the complete combustion of $900 \ g$ of glucose is:
[Molar mass of glucose in $g \ mol^{-1} = 180$]