I'm aware that in Gray code the successive numbers will differ only by one bit. However I'm not able to proceed further.
The question is asking you the value of N where the value of Gx = 1 for N+1.
Map the current state N and Next state N+1 for the 4 bit Gray code
Read off the min term for each next case of Gx = 1
G0 = 0.1.6.7.184.108.40.206
G1 = 220.127.116.11.18.104.22.168
G2 = 22.214.171.124.126.96.36.199
G3 = 188.8.131.52.14.10.11
--> Answer = G2 is correct though they have the terms out of order in the question