unstable ?

a

Disclaimer: All the statements written below are purely the work of my imagination and cant guarantee any relation to known facts.

Look at your own risk

Thinking (A)

stronger acids => more unstable (as more dissociation)
(horribly wrong statement I hope)

therefore A

I say (a)

Because I think the other options r stabilized due to + I effect

My reason may be wrong Din't revise organic yet : (

i will also go with (A) because it has two adjacent c=o bonds......so it will be unstable.

How does that make alpha-keto acid unstable?

I don't think we can use conjugate base concept here...that is to decide acidity. On warming(not even full-on heating), beta-keto acids quickly decarboxylate by means of six-membered transition state. So I go for (b)..can't think of anything else.
Eure please confirm.

wat abt Mesomeric effect guys ???

haha!!!!!!!i was damn sure i got this wrong [1][1][1]