The correct option is B - TSPO.

[as per provisional answerkey]

Solution

To solve this coding-decoding problem, we must first identify the pattern used to transform "ZERO" into "ADSN". Let's examine the alphabetical position of each letter and the shift applied:
1. Z to A: Z is the 26th letter. Moving 1 step forward (circularly) gives A. (Shift: +1)
2. E to D: E is the 5th letter. Moving 1 step backward gives D. (Shift: -1)
3. R to S: R is the 18th letter. Moving 1 step forward gives S. (Shift: +1)
4. O to N: O is the 15th letter. Moving 1 step backward gives N. (Shift: -1)
The pattern is a repeating sequence of +1, -1, +1, -1.

Now, apply the same logic to the word STOP:
1. S (+1): The letter after S is T.
2. T (-1): The letter before T is S.
3. O (+1): The letter after O is P.
4. P (-1): The letter before P is O.
Combining these, we get TSPO.

Why the other options are incorrect

Option (a) - SPOT: This is simply an anagram of the original word and does not follow the +1, -1 mathematical shift pattern established by the example.
Option (c) - TSOP: This option correctly identifies the first two letters (T and S) but fails to apply the +1 shift to 'O' and the -1 shift to 'P', essentially leaving the last two letters in their original positions.
Option (d) - POST: This is another anagram of the word "STOP" and ignores the alphabetical shifting logic required for the code.

Key Concept

This question tests the "Alternating Letter Shift" pattern, where each character in a string is transformed using a consistent sequence of addition and subtraction based on its position in the alphabet.