A two letter series is given with one term missing: CX, EV, GT, IR, ?. Which of the following pairs of letters should replace the question mark so that the alphabetic pattern continues correctly?

Introduction / Context:
This question provides a sequence of two letter groups: CX, EV, GT, IR, and a missing term. The task is to find the pair of letters that fits the pattern. Such problems test understanding of bidirectional movement in the alphabet and reinforce skills in identifying regular changes in letter positions for reasoning and aptitude examinations.

Given Data / Assumptions:

• Known pairs: CX, EV, GT, IR.
• Each pair consists of two capital letters.
• We expect the first and second letters to follow separate but consistent patterns across the series.
• Alphabet positions: A is 1, B is 2, and so on.
• Options: LP, LQ, KP, KQ.

Concept / Approach:
We treat each position separately: the first letters C, E, G, I form one sequence, and the second letters X, V, T, R form another. By converting letters into their numerical positions, we identify the step size in each sequence. The missing pair is then obtained by applying the same step to the latest term in each of the two sub sequences.

Step-by-Step Solution:
Step 1: Convert the first letters to numbers: C(3), E(5), G(7), I(9).Step 2: Observe the differences: 3 to 5 is +2, 5 to 7 is +2, and 7 to 9 is +2. Thus, the first letter increases by 2 each time.Step 3: Apply this rule to I(9) by adding 2, which gives 11, corresponding to the letter K.Step 4: Now convert the second letters: X(24), V(22), T(20), R(18).Step 5: Observe the pattern: 24 to 22 is -2, 22 to 20 is -2, and 20 to 18 is -2. So the second letter decreases by 2 each time.Step 6: Apply this to R(18). Subtracting 2 gives 16, which is the letter P.Step 7: Combining the results for both positions, the next pair must be KP.

Verification / Alternative check:
Writing out the extended series of first letters gives C, E, G, I, K, with each step being +2. The second letters form X, V, T, R, P with each step of -2. No other letter pair from the options satisfies both of these patterns simultaneously. Therefore KP is the consistent continuation of the double sequence.

Why Other Options Are Wrong:
LP would require the first letter to move from I(9) to L(12), which is a step of +3 rather than +2. LQ and KQ also produce incorrect steps for the second letter; 18 to 17 or 18 to 17 would break the consistent -2 pattern. Hence, none of these alternatives can be correct.

Common Pitfalls:
Some learners focus only on the first letters or only on the second letters. Others try to visually guess the next pair without using numerical positions. A robust approach is to treat each column of letters as its own simple arithmetic sequence and extend both consistently.

Final Answer:
The pair of letters that correctly completes the series is KP.