S1: pumping lemma is a negativity test which is used to prove that a language isn't regular. If a language doesn't satisfy the pumping lemma, then it is definitely not regular.. But if a language satisfies the pumping lemma, it may be regular or may not be regular. So S1 is false.
S2: given a grammar, if all the production rules of the grammar of the form A->aB or A->b or A->Ba where {a, b} are terminals and {A, B} are non terminals, then the grammar is a regular grammar, otherwise the grammar isn't regular. So as we have an algorithm by which we are able to decide whether a grammar is regular or not, so this is decidable. So S2 is true.
S3: suppose L=$\phi$ which is a regular language and M ={anbn|n>=0} which is a context free language, then L.M is $\phi$ which is regular. So S3 is false.
Hence answer is (b) only S2 is correct