Assertion : Change in colour of acidic solution of potassium dichromate by breath is used to test drunk drivers. Reason : Change in colour is due to the complexation of alcohol with potassium dichromate.

• A

  If both assertion and reason are true and reason is the correct explanation of the assertion
• B

  If both assertion and reason are true but reason is not the correct explanation of the assertion
• Correct answer
  C

  If assertion is true, but reason is false
• D

  Both assertion and reason are false statements.

Solution

Change in colour is due to the oxidation of alcohol with potassium dichromate. Oxidation of alcohols with $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ in dilute $\mathrm{H}_2 \mathrm{SO}_4$ (orange solution):
$\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ in presence of dilute $\mathrm{H}_2 \mathrm{SO}_4$ acts as an oxidising agent. It is converted into chromic sulphate which is green in colour. $$ \begin{gathered} \mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7+4 \mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{K}_2 \mathrm{SO}_4+\mathrm{Cr}_2\left(\mathrm{SO}_4\right)_3+4 \mathrm{H}_2 \mathrm{O}+\frac{3}{2} \mathrm{O}_2 \\ \text { (orange) } \end{gathered} $$ (green)

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