In the alphabet pair series AC, EG, ?, MO, which of the following pairs of letters should replace the question mark to complete the pattern correctly?

Introduction / Context:
This question is based on an alphabet pair series. We are given the sequence AC, EG, ?, MO and asked to choose the missing pair that keeps the pattern consistent. In such problems the positions of letters in the English alphabet are treated like numbers, and the candidate must discover how each letter progresses across the terms. Recognising whether the pattern is a constant difference or a repeated jump is the main skill being tested.

Given Data / Assumptions:

• Known terms in order: AC, EG, ?, MO.• Each term consists of two letters.• The first letters form the sub series A, E, ?, M.• The second letters form the sub series C, G, ?, O.• Alphabet positions: A=1, B=2, ..., Z=26.

Concept / Approach:
The natural approach is to examine the first letters alone and then the second letters alone. If a constant increment is seen in both sub series, we can apply that increment to find the missing term. Because the visible jumps from A to E and from C to G already suggest equal steps in both positions, we expect that the same increment will apply again, leading us directly to the required pair of letters.

Step-by-Step Solution:
Step 1: Convert first letters to numbers: A=1 and E=5.Step 2: The difference between 1 and 5 is +4.Step 3: We know the next first letter after the missing pair is M=13. To check consistency, assume that the pattern is +4 each time, so the series should be 1, 5, 9, 13.Step 4: Indeed, 9 + 4 = 13, so the missing first letter must be the letter at position 9, which is I.Step 5: Now consider the second letters: C=3 and G=7.Step 6: Here the difference is also +4, so the second letters should follow 3, 7, 11, 15.Step 7: Position 11 corresponds to K and position 15 corresponds to O. The known last second letter O confirms this pattern.Step 8: Therefore, the missing pair must be IK.

Verification / Alternative check:
Write the entire series in numeric form as pairs of positions: AC=(1,3), EG=(5,7), IK=(9,11), MO=(13,15). In both coordinate positions, the differences are consistently +4 from one term to the next. This double check across both letters ensures that IK is not an accidental fit but the unique solution that preserves the underlying rule.

Why Other Options Are Wrong:
IJ, IL and IM all share the correct first letter I but incorrect second letters. For IJ, J is position 10, giving a second letter sequence 3, 7, 10, 15, which breaks the +4, +4, +4 pattern. IL would give 3, 7, 12, 15 and IM would give 3, 7, 13, 15, both of which are inconsistent as well. Because the pattern is a strict +4 increment in both positions, only IK satisfies the requirement perfectly.

Common Pitfalls:
Some students identify the pattern for the first letters only and then choose any option with the correct starting letter, ignoring the second letters. Others may see that the second letters appear to be increasing but do not verify the exact increment. To avoid errors in alphabet series questions, always check the numeric pattern separately for each letter position in the pair or triplet.

Final Answer:
IK