The average molecular weight of the air which has $21 \%$ of $O_2$ and $79 \%$ of $N_2$, is

What is the mass in gram of $1$ atom of an element if its atomic mass is $10 \ u$?

The phosphate of a metal has the formula $MPO_4$. The formula of its nitrate will be

Complete reaction of $2.0 \, g$ of calcium (at. wt. $= 40$) with excess $HCl$ produces $1.125 \, L$ of $H_2$ gas. Complete reaction of the same quantity of another metal $M$ with excess $HCl$ produces $1.85 \, L$ of $H_2$ gas under identical conditions. The equivalent weight of $M$ is closest to

$0.126 \ g$ of an acid requires $20 \ mL$ of $0.1 \ N$ $NaOH$ for complete neutralization. The equivalent weight of the acid is:

Calculate the molecular mass of the following:
$(i)$ $H_{2}O$
$(ii)$ $CO_{2}$
$(iii)$ $CH_{4}$