What is IUPAC name of acrolein?

What is IUPAC name of acrolein?
  1. Prop-2-enal
  2. 2-methyl but-2-enal
  3. 3-methyl but-2-enal
  4. But-2-enal

Asked in: MHT CET 2020 (14 Oct Shift 2)

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