the correct answer is option a
main memory size = 128 kb = 2 ^7 * 2^10 = 2^17 bytes
cache memory size = 2 kb = 2^10 bytes
no of lines = 16 bytes
cache offset = cache memory size \ no of lines = 2^10\2^4 = 2^6 bytes
number of bits in cache offset = 6 bits
as total main memory size = 17 bits
tag bits = 17 - 6 = 11 bits