Brown colour in $\mathrm{HNO}_{3}$ can be removed by

Brown colour in $\mathrm{HNO}_{3}$ can be removed by
  1. adding Mg powder.
  2. boiling the acid.
  3. passing $\mathrm{NH}_{3}$ through acid.
  4. passing air through warm acid.

Solution

Nitric acid decomposes to give $\mathrm{NO}_{2}$ which is brown
$4 \mathrm{HNO}_{3} ightarrow 4 \mathrm{NO}_{2}+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}$
When air is passed through acid the reaction proceeds towards left hand side and brown colour diminishes.

Asked in: JEE-TOPICTESTS-CHEMISTRY

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