Which of the following is not an example of redox reaction?

1. $\mathrm{CuO}+{\mathrm{H}}_{2}\to \mathrm{Cu}+{\mathrm{H}}_{2}\mathrm{O}$

2. ${\mathrm{Fe}}_{2}{\mathrm{O}}_{3}+3\mathrm{CO}\to 2\mathrm{Fe}+3{\mathrm{CO}}_{2}$

3. $2\mathrm{K}+{\mathrm{F}}_{2}\to 2\mathrm{KF}$

4. ${\mathrm{BaCl}}_{2}+{\mathrm{H}}_{2}{\mathrm{SO}}_{4}\to {\mathrm{BaSO}}_{4}+2\mathrm{HCl}$

Hint: Redox reaction = oxidation-reduction reaction

Following reactions are the example of redox reaction

$\mathrm{CuO}+{\mathrm{H}}_{2}\to \mathrm{Cu}+{\mathrm{H}}_{2}\mathrm{O}$

${\mathrm{Fe}}_{2}{\mathrm{O}}_{3}+3\mathrm{CO}\to 2\mathrm{Fe}+3{\mathrm{CO}}_{2}$

$2\mathrm{K}+{\mathrm{F}}_{2}\to 2\mathrm{KF}$

Option (d) is not an example of redox reaction because it is an example of double displacement reaction.