Middle term of repeating letter sequence

Analyze the letter frequency pattern starting from the end of the alphabet :

Following this arithmetic progression, each letter k positions from Z appears (k + 2) times.

The total number of terms in the sequence across all 26 letters of the alphabet is: Total = 2 + 3 + 4 + \dots + 27 = 27 × 28/2 - 1 = 378 - 1 = 377 terms.

The index of the exact middle term is: 377 + 1/2 = 189 .

We need to find which letter covers the 189th position by accumulating counts from Z downwards:

Since the 189th position lands exactly on the last occurrence of the letter I, the middle term is I.

Answer: (b).