Equivalent weight of crystalline oxalic acid is

What is the atomic mass of $Fe$?
Given abundance of ${}^{54}Fe = 10\%$,${}^{56}Fe = 85\%$,and ${}^{57}Fe = 5\%$.

The equivalent weight of $Zn(OH)_2$ in the following reaction is equal to its: $Zn(OH)_2 + HNO_3 \to Zn(OH)(NO_3) + H_2O$

$A$ metal oxide contains $32\%$ oxygen by mass. Its equivalent mass is:

The equivalent weight of an acid:

An element has two main isotopes of mass numbers $85$ and $87$. In nature,they occur in the ratio of $75\%$ and $25\%$ respectively. The atomic weight of the element will be approximately: