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

Explain the concept of Average Atomic Mass.

$0.84 \, g$ of a metal hydride contains $0.04 \, g$ of hydrogen. What is the equivalent mass of the metal?

The equivalent weights of $H_3PO_4$ in the following reactions are respectively:
$H_3PO_4 + OH^{-} \rightarrow H_2PO_4^- + H_2O$
$H_3PO_4 + 2OH^{-} \rightarrow HPO_4^{2-} + 2H_2O$
$H_3PO_4 + 3OH^{-} \rightarrow PO_4^{3-} + 3H_2O$

Calculate the molecular mass of glucose $[C_{6}H_{12}O_{6}]$ molecule. (in $u$)

If the weight of $1 \ L$ of a gas is $2 \ g$,then its vapor density and molecular weight are respectively .....