The equivalent weight of an acid is equal to

An alloy of metals $X$ and $Y$ weighs $12 \ g$ and contains atoms $X$ and $Y$ in the ratio of $2:5$. The percentage of metal $X$ in the alloy is $20$ by mass. If the atomic mass of $X$ is $40$,what is the atomic mass of metal $Y$ (in $amu$)?

At $STP$,if $5.6 \ L$ of a gas weighs $7.5 \ g$,then identify the gas.

The relative abundance of two isotopes of atomic weight $85$ and $87$ is $75\%$ and $25\%$ respectively. The average atomic weight of the element is:

In Victor Mayer’s method,$0.2 \ g$ of an organic substance displaced $56 \ mL$ of air at $STP$. The molecular weight of the compound is:

Naturally occurring boron consists of two isotopes with atomic masses $10.01 \ (I)$ and $11.01 \ (II)$. The average atomic mass of natural boron is $10.81$. Find the percentage abundance of isotopes $(I)$ and $(II)$ respectively.