Which of the following is not decidable?

GATE · Computer Science · 1997

1. A.

   Given a Turing machine M, a string s and an integer k, M accepts s within k steps

2. B.

   Equivalence of two given Turing machines

3. C.

   Language accepted by a given finite state machine is not empty

4. D.

   Languages generated by a context free grammar is non empty

Attempted by 105 students.