Option D is correct
Both the compound are aldehyde showing reducing property. So they ca not be distinguished by Fehling' solutiin or Tolkien'* reagent. Again they cannot be distinguished by 2,4DNP solution which detects the presence carbonyl group.Here both compounds respond to this reagent.
Reagents used inD detect the presence of keto-methylje group present in carbonyl compound. Here actaldhydeac responds to this test but formaldhyde does not.
