Which method is used to determine atomic mass accurately?

If $1.0 \ g$ of a metal combines with $8.89 \ g$ of bromine,what is the approximate equivalent weight of the metal? (Given: Atomic weight of $Br = 80 \ g/mol$)

The equivalent mass of an element $X$ is $9$. If the vapor density of its chloride salt is $66.75$,determine the valency of element $X$.

Hydrazine reacts with $KIO_3$ in the presence of $HCl$ as:
$N_2H_4 + IO_3^- + 2H^+ + Cl^- \rightarrow ICl + N_2 + 3H_2O$
The equivalent masses of $N_2H_4$ and $KIO_3$ respectively are:

If the molecular mass and atomic mass of sulphur are $256$ and $32$ respectively,its atomicity is:

If $1.2 \, g$ of a metal displaces $1.12 \, L$ of hydrogen at $STP$,the equivalent weight of the metal would be: