Aldehydes do not interact with: 1 hydrogen, 2 copper hydroxide (2), 3 ammonia solution of silver oxide (1), 4 methane.

1. Reaction of interaction of aldehydes with hydrogen (reduction of aldehydes to primary alcohols):

RHCO + H2 = RCH2OH. This reaction takes place by heating and in the presence of catalysts.

2. The reaction with copper hydroxide is a qualitative reaction to aldehydes, as a result of which a blue suspension of copper hydroxide, when heated with aldehydes, gives an orange-red precipitate of copper oxide:

RHCO + 2Cu (OH) 2 = RCOOH + Cu2O + 2H2O.

3. The reaction with an ammoniacal solution of silver oxide is a qualitative reaction to aldehydes, called the “silver mirror reaction”, as a result of which a “mirror” coating of silver appears on the walls of the test tube:

RHCO + [Ag (NH3) 2] OH = RCOONH4 + Ag + NH3 + H2O. This reaction takes place by heating.

4. Methane is a low-reactive compound and does not react with aldehydes.

Answer: 4 – methane.