$A$ gas has the formula $(CO)_x$. Its vapour density is $70$. What is the value of $x$?

If the equivalent mass of a metal with a valency of $+2$ is $12$,then the molar mass of its oxide is:

The relative abundances of two isotopes of rubidium with atomic masses $85$ and $87$ are $75\%$ and $25\%$ respectively. What is the average atomic mass of rubidium (in $.5$)?

One gram of hydrogen is found to combine with $80 \ g$ of bromine. One gram of calcium (valency $= 2$) combines with $4 \ g$ of bromine. The equivalent weight of calcium is:

Naturally occurring boron has $20\%$ $_5B^{10}$ and $80\%$ $_5B^{11}$. The average atomic weight of boron is

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