Which of the following terms correctly replaces the question mark (?) in the series given below?

A1, C4, E9, G16, ?, K36

The correct option is I25.

To determine the term that replaces the question mark (?) in the series A1, C4, E9, G16, ?, K36, we can break down the series into two parts: the alphabetical pattern and the numerical pattern.

1. Alphabetical Pattern:
Let us examine the position of each letter in the English alphabet:
A is the 1^st letter.
C is the 3^rd letter (1 + 2 = 3).
E is the 5^th letter (3 + 2 = 5).
G is the 7^th letter (5 + 2 = 7).
Notice that each consecutive term skips one letter (adding +2 to the alphabetical position).
Following this pattern:
The next position will be 7 + 2 = 9.
The 9^th letter of the alphabet is I.
We can verify this with the next given letter, K, which is at position 9 + 2 = 11 (the 11^th letter).

2. Numerical Pattern:
Let us analyze the sequence of numbers: 1, 4, 9, 16, ?, 36.
Each number corresponds to the square of consecutive natural numbers:

$1^2=1$

$2^2=4$

$3^2=9$

$4^2=16$

Following this sequence, the missing number is the square of 5:

$5^2=25$

We can verify the last term with the square of 6:

$6^2=36$

Combining the letter I and the number 25 gives the complete missing term I25.