Chip select for the ROM
Image the address is 0x4000. Option (B) gives 0.1.(0+0)=0. The chip is selected even though the address is outside the range. You need to check not just if the options will give 0 for addresses in-range, but 1 for addresses outside the range.

Moreover, A12 is address line for the ROM so how can we use it for CS signal.

I don't understand fully, but the line coming out of the 8085 can be split into two traces, and connected to both the ROM and the CS generating circuit.