Consider the redox reaction $2{\mathrm{S}}_2{{\mathrm{O}}_3}^{2-}+{\mathrm{I}}_2\stackrel{}{\to }{\mathrm{S}}_4{{\mathrm{O}}_6}^{2-}+2{\mathrm{I}}^{–}$.

The table below gives the results of three titration carried out with $0.200 \mathrm{M} \mathrm{HCl}$. To determine the molarity of a given $\mathrm{NaOH}$ solution using phenolphthalein as indicator. $\mathrm{NaOH}$ was taken in the burette and $\mathrm{HCl}$ was taken in a conical flask for the titration.

$\begin{array}{|llll|}\hline \mathrm{TitrationNo}. & {\mathrm{V}}_{\mathrm{HCl}\left(\mathrm{mL}\right)}& {\mathrm{V}}_{\mathrm{NaOH} \left(\mathrm{mL}\right)}& {\mathrm{M}}_{\mathrm{NaOH}mold{\mathrm{m}}^{-3}}\\ \mathrm{I}& 21.4& 19.3& 0.222\\ \mathrm{II}& 18.6& 16.8& 0.221\\ \mathrm{III}& 22.2& 21.1& 0.210\\ \hline\end{array}$

The actual molarity of the prepared $\mathrm{NaOH}$ solution was $0.220 {\mathrm{moldm}}^{-3}$. Which among the following could be the reason for the wrong value obtained in titration $\mathrm{III}$?

The equivalent weight of a metal is double that of oxygen. How many times is the weight of its oxide greater than weight of the metal?

$\mathrm{x}$ millimoles of ${\mathrm{KMnO}}_4$ reacts completely with $\mathrm{y}$ millimoles of ${\mathrm{MnSO}}_4$ in the presence of fluoride ions, to give ${\mathrm{MnF}}_4$ quantitatively. Then

The amount of wet $\mathrm{NaOH}$ containing $15\%$ water required to prepare $70$ litres of $0.5 \mathrm{N}$ solution is

$28{{\mathrm{NO}}_3}^{–}+3{\mathrm{As}}_2{\mathrm{S}}_3+4{\mathrm{H}}_2\mathrm{O}\to 6{{\mathrm{AsO}}_4}^{3–}+28\mathrm{NO}+9{{\mathrm{SO}}_4}^{2–}+8{\mathrm{H}}^{+}.$

What is the equivalent mass of ${\mathrm{As}}_2{\mathrm{S}}_3$ in the above reaction (molecular mass of ${\mathrm{As}}_2{\mathrm{S}}_3=\mathrm{M}$)?