Which one of the following will come in please of the question mark(?) CD, HI, MN,?

Convert each letter to its alphabet position. CD is C(3), D(4). HI is H(8), I(9). MN is M(13), N(14). Each letter moves forward by exactly 5 places from one pair to the next: C to H is +5, D to I is +5, H to M is +5, I to N is +5. Applying the same +5 shift to M and N gives R and S, so the missing pair is RS, option D.

• A) QS is wrong. Q is M+4, so the first letter breaks the +5 pattern.
• B) OP is wrong. O is M+2 and P is N+2, so the step is +2, not +5.
• C) PQ is wrong. P is M+3 and Q is N+3, so the step is +3.

The core concept is a letter-series with a uniform alphabetical shift. It is a pure reasoning skill, and converting letters to numbers is the habit that makes such series fast and reliable in the reasoning section of the exam.

Trap: checking only the first letters, or assuming a shift of +1 or +2 because the pattern looks alphabetical. Always verify the shift against both letters of every given pair before choosing.