Directions: Choose the correct alternative from the given ones that will…

Concept: An alternating (interleaved) series is formed by threading two independent single-letter sequences together — the terms at the odd positions (1st, 3rd, 5th, ...) form one sequence, and the terms at the even positions (2nd, 4th, 6th, ...) form another, each advancing by its own fixed step. To find any missing term, first separate the series into these two threads, then extend each thread using its own pattern.

Application:

1. The 1st, 3rd, 5th and 7th terms are A, C, E, G — an odd-position thread advancing by 2 letters at each step (A to C to E to G).

2. The 2nd, 4th and 6th terms are P, Q, R — an even-position thread advancing by 1 letter at each step (P to Q to R).

3. The 8th term is the next value of the even-position thread after R, and the 9th term is the next value of the odd-position thread after G.

4. Extending the even-position thread by 1 letter after R gives S; extending the odd-position thread by 2 letters after G gives I.

Cross-check: Using alphabet positions (A = 1, ..., Z = 26): the odd-position thread A(1), C(3), E(5), G(7) increases by 2 each time, so the next value is 7 + 2 = 9, which is I. The even-position thread P(16), Q(17), R(18) increases by 1 each time, so the next value is 18 + 1 = 19, which is S. Both checks agree, confirming that the 8th and 9th terms are S and I.

Hence, the pair S I correctly completes the series.