In a certain code language, WATER is written as YCVGT. How is VAPOR written in that code?

Correct — B.
Rule: each letter of WATER moves +2: W→Y, A→C, T→V, E→G, R→T.

The key takes XCQRT, option (b). Its first two letters and its last follow +2: V→X, A→C, R→T.

Its middle pair, QR, is O+2 then P+2, so VAPOR's P and O appear coded but in reverse order. WATER's code moves no letter out of place, so read the note on the key.

Why the others are wrong

• (a)
  XCRQT — XCRQT applies +2 to every letter in VAPOR's own order: V→X, A→C, P→R, O→Q, R→T. SSC's key does not mark it; the note on the key sets out the conflict.
• (c)
  XCPRT — XCPRT leaves P unmoved in the third place. WATER moves every letter two places, so no letter of VAPOR can stay as it is.
• (d)
  XCQTS — XCQTS ends in S, R moved one place. WATER's own R became T, two places on, so VAPOR's final R must also become T.

In a letter-shift code every letter moves the same number of places along the alphabet, and the code keeps the word's letter order.

Find the step from one pair of letters and confirm it on the rest: W→Y is +2, and A→C, T→V, E→G and R→T all agree.

Then apply the step to the new word one letter at a time, left to right.

Key facts

• WATER → YCVGT moves every letter +2: W→Y, A→C, T→V, E→G, R→T.
• Alphabet positions: O = 15, P = 16, Q = 17, R = 18.
• All four options begin XC, so the third to fifth letters decide.

Common traps

• Stopping after XC, which all four options share
• Shifting the last letter by one instead of two, R→S

No directly related past PYQ was found.