In the reaction $2Na_2S_2O_3 + I_2 \to Na_2S_4O_6 + 2NaI$,the equivalent weight of $Na_2S_2O_3$ (molecular weight = $M$) is equal to:

Statement $1$: The equivalent mass of $Cu$ in $CuO$ is $63.6$ and in $Cu_2O$ is $31.8$. Statement $2$: Equivalent mass = $\frac{\text{Molecular mass}}{\text{Valency}}$

Match column $-I$ and column $-II$ with the correct molar mass values:

Column $-I$	Column $-II$
$(i)$ Barium sulphate	$(a)$ $1877 \ g/mol$
$(ii)$ Magnesium pyrophosphate	$(b)$ $235 \ g/mol$
$(iii)$ Ammonium phosphomolybdate	$(c)$ $188 \ g/mol$
$(iv)$ Silver chloride	$(d)$ $222 \ g/mol$
$(v)$ Silver bromide	$(e)$ $143.5 \ g/mol$
$(vi)$ Silver iodide	$(f)$ $233 \ g/mol$

Equivalent weight of crystalline oxalic acid is ...........

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

$16.25 \ g$ of metal chloride is obtained on complete conversion of $8 \ g$ of metal oxide into metal chloride. What will be the equivalent weight of the metal?