In a code language “BEST” is written as “BEQV” and “NINE” is written as “FQBQ”, then code for “FOUR” will be
A.RCUR
B.RCOX
C.ILPX
D.LIQX

Hint: The given question is of code solving in logical reasoning section, first we have to find a relation on the first set of data given to us then we will check if our reasoning for deciphering the first set was correct by checking on the second set if the reasoning comes out to be sound we will then apply that rule to our asked question to get the answer. We see in the second set “NINE” comes out to be “FQBQ” that means that the first and third letter will result in the second and fourth letter in the resultant set. Thus first letter gives second , second gives first , third gives fourth and fourth gives third.
We also try to find the relation by seeing how many increments happen in the resultant,
 $ N \to + 3 \to Q $
 $ I \to - 3 \to F $
Just by trying to find these relations we will get our answer.

Complete step by step solution:
We see in the second set “NINE” comes out to be “FQBQ” that means that first and third letter will result in the second and fourth letter in the resultant set. Thus first letter gives second , second gives first , third gives fourth and fourth gives third.
Then we see in the second given set, for first and second positions
 $ N \to + 3 \to Q $
 $ I \to - 3 \to F $
For third and fourth positions,
 $ N \to + 3 \to Q $
 $ E \to - 3 \to B $
We see on applying this to first set as well
 $ \begin{gathered}
  B \to + 3 \to E \\
  E \to - 3 \to B \\
  S \to + 3 \to V \\
  T \to - 3 \to Q \\
\end{gathered} $
Hence our reasoning is correct.
For getting our answer, we write,
 $ \begin{gathered}
  F \to + 3 \to I \\
  O \to - 3 \to L \\
\end{gathered} $
Thus first two letter are LI
Since only one option contains it that option is D. which is our correct answer.
So, the correct answer is “Option D”.

Note: Always after getting a rule for breaking the code do check it on another given set of input and output to get a solid proof that our reasoning and assumption is correct.