Q33 / 180 · AIIMS 2012 · Chemistry

Which is not stable under ambient condition?

  • A
    $\mathrm{TiO}_2, \mathrm{Ti}^{+4}$
  • B
    $\mathrm{VO}, \mathrm{V}^{+4}$
  • C
    $\mathrm{VO}_2, \mathrm{~V}^{+5}$
  • Correct answer
    D
    $\mathrm{Cu}_2 \mathrm{O}, \mathrm{Cu}^{+2}$

Solution

Copper (I) compounds are unstable in aqueous solution and undergo disproportio-nation. $2 \mathrm{Cu}^{+} \rightarrow \mathrm{Cu}^{2+}+\mathrm{Cu}$ The greater stability of $\mathrm{Cu}^{2+}{ }_{(a q .)}$ than $\mathrm{Cu}^{+}{ }_{(a q .)}$ is due to much more $-v e \Delta_{h y d} H$ of $\mathrm{Cu}^{2+}{ }_{(a q .)}$ than $\mathrm{Cu}_{(a q .)}^{+}$, which compensates for the second ionisation enthalpy of $\mathrm{Cu}$.

Hence, the correct answer is option: 'D'.

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