Find the odd pair of letters from the following alternatives based on the fixed backward step in the alphabet.

Introduction / Context:
This question checks your ability to see simple letter pair patterns in the English alphabet. Many odd man out problems use constant forward or backward steps between letters, and you must spot which pair breaks the rule.

Given Data / Assumptions:

• Letter pairs: CA, FD, KI, TQ.
• We use alphabet positions A = 1, B = 2, ..., Z = 26.
• We look for a common difference between the first and second letter in each pair.

Concept / Approach:
The approach is to convert each letter to its numeric position and compute second minus first. If three pairs show the same difference and one differs, the differing pair is the odd one out. Here we will look specifically at backward steps from first to second letter.

Step-by-Step Solution:
CA: C = 3, A = 1, so the difference is 1 minus 3 = -2. FD: F = 6, D = 4, so the difference is 4 minus 6 = -2. KI: K = 11, I = 9, so the difference is 9 minus 11 = -2. TQ: T = 20, Q = 17, so the difference is 17 minus 20 = -3. Thus three pairs follow a constant backward step of -2, but TQ has a backward step of -3.

Verification / Alternative check:
You can also quickly check by counting letters backward. From C to A, F to D, and K to I, you go back two letters each time. From T to Q, however, you pass R and S and then reach Q, which is three steps back. This visual or mental counting way confirms that TQ does not share the same fixed step as the other pairs.

Why Other Options Are Wrong:

• CA: Second letter is two positions before the first, matching the common rule.
• FD: Again, D is two letters before F, so it fits the pattern.
• KI: I lies two positions before K, so it also follows the same backward step.

Common Pitfalls:
A common mistake is to look only at rough proximity in the alphabet and assume all pairs are similar. Without explicitly counting the steps, the difference between -2 and -3 can go unnoticed. Always calculate or count letter movements carefully when solving alphabet series questions.

Final Answer:
TQ