If in a certain code, 'TRUTH' is written as 'UQSVI', how is 'FALSE' written?

Correct — B.
Rule: shift by position: +1, −1, −2, +2, +1.

TRUTH: T→U (+1), R→Q (−1), U→S (−2), T→V (+2), H→I (+1)
FALSE: F→G, A→Z (−1 wraps past A), L→J, S→U, E→F

That reads GZJUF → option (b).

Why the others are wrong

• (a)
  GXMTF — GXMTF sends A back three to X and moves L forward to M. The pair asks −1 at letter 2 (R → Q) and −2 at letter 3 (U → S), giving Z and J.
• (c)
  GPLTF — GPLTF leaves L as L and moves S only one place, to T. In TRUTH the third letter moves back two (U → S) and the fourth forward two (T → V), so L → J and S → U.
• (d)
  GQLTF — GQLTF turns A into Q, a jump no step of the rule makes. Letter 2 moves −1, so A wraps round to Z. Its L (unchanged) and T (S + 1) also miss the −2 and +2.

This is a position-wise shift code: each letter moves along the alphabet by an amount set by its place in the word, not by which letter it is.

The proof sits inside TRUTH itself. Its two Ts become U (first letter, +1) and V (fourth letter, +2). A letter-for-letter substitution would code both Ts the same way.

Key facts

• Shift pattern here: +1, −1, −2, +2, +1 across the five positions.
• A repeated letter coded two ways (T → U, then T → V) proves the code works by position.
• Backward wrap: A − 1 = Z, A − 2 = Y.

Common traps

• Coding a repeated letter the same way both times because it looks the same
• Moving A forward, or leaving it, instead of wrapping back to Z on a −1 step

No directly related past PYQ was found.