sblock Elements - Result Question 12
####8. A metal on combustion in excess air forms $X . X$ upon hydrolysis with water yields $H _2 O _2$ and $O _2$ along with another product. The metal is
(2019 Main, 12 Jan I)
(a) $Li$
(b) $Mg$
(c) $Rb$
(d) $Na$
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Answer:
Correct Answer: 8. (b)
Solution:
- Metal $(A)$ is rubidium $(Rb)$. In excess of air, it forms $RbO _2(X)$. $X$ is a superoxide that have $O _2^{-}$ion. It is due to the stabilisation of large anion by large cations through lattice energy effects. $RbO _2(X)$ gets easily hydrolysed by water to form the hydroxide, $H _2 O _2$ and $O _2$.
The reaction involved are as follows:
$$ \begin{aligned} & Rb+O _2 \longrightarrow \underset{(X)}{RbO _2} \text { (superoxide) } \ & \underset{(X)}{2 RbO _2+2 H _2 O} \longrightarrow 2 RbOH+H _2 O _2+O _2 \end{aligned} $$
