A series of letter pairs is given with one pair missing. Select the option that continues the pattern: BB, DZ, GW, KS, ?

Introduction / Context:
This alphabet series uses letter pairs whose first letters move forward in increasing steps, while the second letters move backward in increasing steps. You need to find the next pair that respects both of these evolving patterns. This kind of two way movement is common in reasoning questions.

Given Data / Assumptions:

• Known pairs: BB, DZ, GW, KS, ? • Alphabet positions: A = 1 to Z = 26. • First letters: B, D, G, K. • Second letters: B, Z, W, S.

Concept / Approach:
We treat the first letters as one numeric sequence and the second letters as another. By using positions, we compute changes from B to D to G to K, and from B to Z to W to S. The pattern reveals steadily increasing step sizes in both directions, which we then extend to find the next letters.

Step-by-Step Solution:
Step 1: Analyze first letters B, D, G, K. Positions: B = 2, D = 4, G = 7, K = 11. Differences: 2 → 4 is +2, 4 → 7 is +3, 7 → 11 is +4. So the increments are +2, +3, +4, meaning the next increment should be +5. Next first letter: 11 + 5 = 16, which is P. Step 2: Analyze second letters B, Z, W, S. Positions: B = 2, Z = 26, W = 23, S = 19. Differences: 2 → 26 is −2 (or +24), 26 → 23 is −3, 23 → 19 is −4. So the negative increments are −2, −3, −4, meaning the next should be −5. Next second letter: 19 − 5 = 14, which is N. Step 3: Combine P and N to form the pair PN.

Verification / Alternative check:
The full numeric patterns are: first letters 2, 4, 7, 11, 16 with increments +2, +3, +4, +5; second letters 2, 26, 23, 19, 14 with increments −2, −3, −4, −5. Both sequences show a clear, steadily increasing magnitude in steps, so PN is the only pair that keeps this structure intact.

Why Other Options Are Wrong:
• IK: First letter I is 9, which does not match the expected next first letter P at position 16. • IG: Both letters I and G fail to fit the +5 and −5 changes predicted by the pattern. • PS: Although P is correct for the first letter, S is 19 and would require no change from the previous second letter, breaking the −5 step.

Common Pitfalls:
Many test takers focus on only the first letters and stop when they see a partial pattern, then pick an option with that first letter but a wrong second letter. Always verify that both positions obey the same type of evolving step rule, especially in two way series like this.

Final Answer:
The letter pair that correctly completes this series is PN.