An aliphatic organic compound(X) containing C, H and N on hydrolysis with dilute HCl to produce formic acid.  'X" is reduced to dimethylamine in presence of Pt (or)  Ni. The compound(X) could be 

Explanation:

1. Hydrolysis with dilute HCl producing formic acid (HCOOH):

   Upon hydrolysis, methyl cyanide (CH₃CN) reacts with water and HCl to form formic acid (HCOOH) as a byproduct:

   CH₃CN + H₂O + HCl → HCOOH

2. Reduction to dimethylamine ((CH₃)₂NH):

   When CH₃CN is reduced in the presence of Pt or Ni, the nitrile group is hydrogenated, forming dimethylamine:

   CH₃CN + H₂ → (CH₃)₂NH

3. Analyzing other options:
   • CH₃NC (Methyl isocyanide): Hydrolysis of CH₃NC produces methylamine and formic acid but does not reduce to dimethylamine.
   • CH₃NH₂ (Methylamine): This does not undergo hydrolysis to produce formic acid.
   • A mixture of CH₃CN and CH₃NC: This would produce a mix of products, which is not supported by the question.

Final Answer:

The compound X is CH₃CN.