In a certain code language, 'RADIO' is written as 'SZEHP' and 'FREQUENCY' is written as 'GQFPVDOBZ'. How will 'TELEVISION' be written in that language?

Correct — A. Number the letters of the word and treat odd and even places differently.

Rule: letters in odd places move +1, letters in even places move −1.

RADIO: R+1=S, A−1=Z, D+1=E, I−1=H, O+1=P, giving SZEHP.
FREQUENCY agrees: F+1=G, R−1=Q, E+1=F, Q−1=P, U+1=V, E−1=D, N+1=O, C−1=B, Y+1=Z.

TELEVISION has ten letters: T+1=U, E−1=D, L+1=M, E−1=D, V+1=W, I−1=H, S+1=T, I−1=H, O+1=P, N−1=M.

That reads UDMDWHTHPM → option (a).

Why the others are wrong

• (b)
  UDMDWHTHOM — UDMDWHTHOM leaves the ninth letter as O. Place 9 is odd, so O must move +1 to P.
• (c)
  UDMDWHTHPN — UDMDWHTHPN keeps the tenth letter as N. Place 10 is even, so N must move −1 to M.
• (d)
  UDMDWHHTPM — UDMDWHHTPM has letters seven and eight the wrong way round. S+1 gives T at place 7 and I−1 gives H at place 8, so the pair reads TH.

An alternating-shift code applies one rule to odd places and another to even places. Nothing is reversed and nothing is rearranged — each letter moves on the spot.

The second worked example is not decoration. RADIO alone would let several rules through; FREQUENCY, at nine letters, is long enough to kill every one but the right one. Always test your rule on it before you code the target word.

Key facts

• In RADIO to SZEHP the shifts run +1, −1, +1, −1, +1.
• In FREQUENCY to GQFPVDOBZ the same alternation holds across all nine letters.
• TELEVISION under that rule is UDMDWHTHPM.
• A − 1 wraps to Z, since A is position 1.

Common traps

• Reading A to Z as an opposite-letter code, which then fails on R to S.
• Losing the place count in a ten-letter word and flipping the sign midway.
• Checking only the first worked example.

No directly related past PYQ was found.