Question

Why formic acid is more stronger than acetic acid?

Answer 1

Formic acid is considered stronger because the CH3 in acetic acid is electron donating but formic acid does not have an electron donating group so its O-H bond is slightly more polarized and more acidic .

Answer 2

because the methyl group is electron donating in the conjugate base of acetic acid, this destabilizes the conjugate base by exacerbating the existing negative formal charge on the deprotonated oxygen, while in formic acid the electron donating methyl is absent in lieu of a hydrogen, which is neither withdrawing nor donating.