Reagent used

@nitu.. if you observe the reaction carefully, the acid has one carbon more. thus the reaction given by you will not answer the question.
I guess the answer to this question is d)None.
As the reaction is methyl carbonylation with takes place in the presence of a metal carbonyl, which is not present in any of the options.
@anirban is it correct?

giv K₂Cr₂O₇ and conc. H₂SO₄ it will oxidise methanol n form acetaldehyde then acetic acid.

The question is asking for one step reaction...i.e. directly acetic acid from methanol!

SOOO... K₂Cr₂O₇ can directly convert alcohols to acids!!

yes your answer is correct @ Subhojit..and the explanation is perfect too..:)

thank you..:)