This question is based on the following words
(Left) VAN RUG PET BOX (Right)
In each of the words, each vowel is changed to the letter immediately following it in the English alphabetical order and each consonant is changed to the letter immediately preceding it in the English alphabetical order. In how many letter-clusters thus formed, will no vowel appear?

Information Given:
(Left) VAN RUG PET BOX (Right)
Rule: Vowel → next letter; Consonant → previous letter.
Vowels: A, E, I, O, U.

Logic:  Transform each letter and check if the resulting cluster has any vowel.

Step-by-step:
VAN → V→U, A→B, N→M → UBM (contains vowel U)
RUG → R→Q, U→V, G→F → QVF (no vowel)
PET → P→O, E→F, T→S → OFS (contains vowel O)
BOX → B→A, O→P, X→W → APW (contains vowel A)

Clusters without vowel: QVF → only one.

Final Answer:
One

Final Correct Option:
B