Correct Answer: IR

Solution : Given:
BY : GT :: DW : ?

Like, BY→B and Y are the opposite letters of each other.
GT→G and T are the opposite letters of each other.
Similarly, DW→D and W are the opposite letters of each other.
Let's check the options –
First option: CF→C and F are not the opposite letters of each other.
Second option: FC→F and C are not the opposite letters of each other.
Third option: PI→P and I are not the opposite letters of each other.
Fourth option: IR→I and R are the opposite letters of each other.

So, only the fourth option follows the same pattern as followed by the given pair. Hence, the fourth option is correct.