Assuming chlorine element has two isotopes as $Cl^{35}$ and $Cl^{37}$ with their percentage abundance as $25\%$ and $75\%$ respectively. Find the average atomic weight.

$A$ metal oxide is reduced by heating it in a stream of hydrogen. It is found that after complete reduction,$3.15 \, g$ of the oxide yielded $1.05 \, g$ of the metal. We may deduce that:

The approximate mass of a tritium oxide molecule is $............$ $amu$.

Among $10^{-9} \ g$ (each) of the following elements,which one will have the highest number of atoms?
Element: $Pb, Po, Pr$ and $Pt$

The equivalent weight of $H_3PO_4$ in the reaction is $Ca(OH)_2 + H_3PO_4 \to CaHPO_4 + 2H_2O$
$(Ca = 40, P = 31, O = 16)$

$A$ mixture of $1.65 \times 10^{21}$ molecules of $X$ and $1.85 \times 10^{21}$ molecules of $Y$ weighs $0.688 \ g$. If the molecular mass of $Y$ is $187 \ g/mol$,what is the molecular mass of $X$?