- A$S_2O_3^{-2}$
- B$S_2O_5^{-2}$
- C$S_2O_6^{-2}$
- ✓$S_2O_7^{-2}$

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$A$. The stability of the hydrides decreases in the order $\mathrm{NH}_3>\mathrm{PH}_3>\mathrm{AsH}_3>\mathrm{SbH}_3>\mathrm{BiH}_3$
$B$. The reducing ability of the hydrides increases in the order $\mathrm{NH}_3<\mathrm{PH}_3<\mathrm{AsH}_3<\mathrm{SbH}_3<\mathrm{BiH}_3$
$C$. Among the hydrides, $\mathrm{NH}_3$ is strong reducing agent while $\mathrm{BiH}_3$ is mild reducing agent.
$D$. The basicity of the hydrides increases in the order $\mathrm{NH}_3<\mathrm{PH}_3<\mathrm{AsH}_3<\mathrm{SbH}_3<\mathrm{BiH}_3$Choose the most appropriate from the option given below:
$\mathrm{Eu}, \mathrm{Cm}, \mathrm{Er}, \mathrm{Tb}, \mathrm{Yb}$ and $\mathrm{Lu}$
$E _{ FeO _4^{2-} / Fe ^{2+}}^\theta$ is $x \times 10^{-3} V$. The value of $x$ is $.........$.