If HELMET is coded as IFMNFU, how is IFMNFU coded?

Correct — A.
Rule: each letter moves +1 (H → I, E → F, L → M, M → N, E → F, T → U).

Apply the same code to IFMNFU:
I → J, F → G, M → N
N → O, F → G, U → V

IFMNFU → JGNOGV → option (a).

Why the others are wrong

• (b)
  JGNNGV — JGNNGV leaves the fourth letter as N. Every letter moves +1, so N becomes O: JGNOGV.
• (c)
  JGNOGU — JGNOGU leaves the last letter as U. It moves +1 like the rest, to V.
• (d)
  JGMOHV — JGMOHV leaves M unshifted and moves F two places to H. Each letter moves exactly one place: M → N, F → G.

HELMET → IFMNFU is a +1 shift at every position. Coding IFMNFU with the same rule moves each letter one place further, so the answer is HELMET shifted +2 in total.

That gives a quick check: H + 2 = J, E + 2 = G, L + 2 = N, M + 2 = O, E + 2 = G, T + 2 = V.

Key facts

• HELMET → IFMNFU moves each letter one place forward.
• IFMNFU → JGNOGV moves each letter one more place.
• JGNOGV is HELMET shifted +2 in total.

Common traps

• Leaving one letter unshifted, as options (b) and (c) do with N and U.
• Moving one letter two places in a single step, as option (d) does with F → H.

No directly related past PYQ was found.