The equivalent weight of phosphoric acid $(H_3PO_4)$ in the reaction $NaOH + H_3PO_4 \to NaH_2PO_4 + H_2O$ is

Oxygen contains $90\%$ of $^{16}O$ and $10\%$ of $^{18}O$. Its atomic mass is

Chlorine has two naturally occurring isotopes,${}^{35}Cl$ and ${}^{37}Cl$. If the atomic mass of $Cl$ is $35.45$,the ratio of natural abundance of ${}^{35}Cl$ and ${}^{37}Cl$ is closest to (in $: 1$)

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

If the equivalent weight of a metal $(M)$ is $x$ and the formula of its oxide is $M_mO_n$,then the atomic weight of $M$ is ......

Elements $A$ and $B$ form two compounds $B_2A_3$ and $B_2A$. $0.05$ moles of $B_2A_3$ weigh $9.0 \ g$ and $0.10$ mole of $B_2A$ weigh $10 \ g$. The atomic weights of $A$ and $B$ are: