Q38 / 225 · JEE Main 2003 · Chemistry

A red solid is insoluble in water. However it becomes soluble if some $\mathrm{KI}$ is added to water. Heating the red solid in a test tube results in liberation of some violet coloured fumes and droplets of a metal appear on the cooler parts of the test tube. The red solid is

  • Correct answer
    A
    $\mathrm{HgI}_2$
  • B
    $\mathrm{HgO}$
  • C
    $\mathrm{Pb}_3 \mathrm{O}_4$
  • D
    $\left(\mathrm{NH}_4\right)_2 \mathrm{Cr}_2 \mathrm{O}_7$

Solution

$\underset{\text { (insoluble) }}{\mathrm{HgI}_2}+\mathrm{KI} \rightarrow \underset{\text { (soluble) }}{\mathrm{K}_2 \mathrm{HgI}_4}$ On heating $\mathrm{HgI}_2$ decomposes as $\mathrm{HgI}_2 \rightleftharpoons \mathrm{Hg}+\mathrm{I}_2$

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

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