Select the option that is related to the fifth term in the same way as the second term is related to the first term and the fourth term is related to the third term.
HELIPAD : HILOPED :: GROUND : GRUAND :: DELIGHT : ?

Let's analyze the logic behind the given pairs:
HELIPAD : HILOPED

The consonants remain in their original positions: H, L, P, D → H, L, P, D.

The vowels (E, I, A) change to the next successive vowel in the standard vowel sequence (A, E, I, O, U):

E → I

I → O

A → E

Thus, HELIPAD becomes HILOPED.

GROUND : GRUAND

Consonants remain unchanged: G, R, N, D → G, R, N, D.

Vowels change to the next vowel:

O → U

U → A (cyclic order of standard vowels)

Thus, GROUND becomes GRUAND.

DELIGHT : ?

Consonants remain unchanged: D, L, G, H, T.

Vowels change to the next vowel in the sequence (A, E, I, O, U):

E → I

I → O

Replacing the vowels gives: DILOGHT