Given: broadcast address of the subnet is given as 163.93.63.255
given address's class is class B (range is 128 to 191 in decimal) and default mask for class B is: 255.255.0.0
Now, in given question, last 2 octet 63.255 will 0 0 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 . Here, in 3rd octet(63) 2 bits are 0 so at least 2 bits from 3rd octet belongs to subnet bits(it can be more than 2).
Now, 192= 1 1 0 0 0 0 0 0
subnet mask value will be(at least) 255.255.192.0 and/or it can be 255.255.224.0 and/or 255.255.240.0 ....and so on
So, C) 255.255.128.0 is not a possible subnet mask