Language accepted by M1 is L1=(00+01+10+11)* and M2 is L2= a*b*.
So L1.L2=(00+01+10+11)* a*b*
In the both the DFA’s of Ques(a) and (b) state A can be final state as there is a null transition from A to C. So making A as final or non final doesn’t change the language accepted by FA.