$1 \ amu$ is equal to

Chlorine exists in two isotopic forms $^{35}Cl$ and $^{37}Cl$. If the average atomic mass of chlorine is $35.5$,what is the percentage abundance of these isotopes respectively?

The equivalent weight of a bivalent metal is $37.2$. The molecular weight of its chloride is

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

Atomic weight of $Ne$ is $20.2$. If $Ne$ is a mixture of $Ne^{20}$ and $Ne^{22}$,what is the percentage abundance of the lighter isotope?

Which one of the following properties of an element is not variable?