In which of the following molecules, $2 \pi$ bonds are present?

In which of the following molecules, $2 \pi$ bonds are present?
  1. $\mathrm{C}_{2} \mathrm{H}_{6}$
  2. $\mathrm{C}_{2} \mathrm{H}_{4}$
  3. $\mathrm{C}_{2} \mathrm{H}_{2}$
  4. $\mathrm{C}_{3} \mathrm{H}_{6}$

Asked in: MHT CET 2020 (13 Oct Shift 2)

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