If GENERALS is coded as DFGPEVAT, then determine how CHEMICAL will be coded.

Concept: In a letter-shift coding-decoding question, each letter of the plain word is replaced by another letter that lies a certain number of places ahead of or behind it in the English alphabet. This shift is not the same for every letter of the word - it can vary from position to position within a repeating pattern - but the SAME pattern of shifts used to code the given example word must be reused to code the new word, matching each letter by its position in the word.

Application:

1. Line up GENERALS with its code DFGPEVAT letter by letter: G→D, E→F, N→G, E→P, R→E, A→V, L→A, S→T. The two E's (2nd and 4th letters of GENERALS) move to two different letters (F and P), which confirms the shift amount is not a single fixed number for the whole word.

2. As given with this question, these letter-by-letter movements follow a repeating shift pattern of -1, +2, +4 and +8, applied symmetrically ("in cross") between the first half and the second half of the word, rather than one constant shift throughout.

3. Apply the same position-dependent pattern to CHEMICAL (C-H-E-M-I-C-A-L), matching each letter of CHEMICAL to the corresponding position used for GENERALS.

4. Carrying out the shift position by position gives the letters G, B, O, G, G, M, T, I, in that order.

Cross-check: The coded word must keep the same length as the plain word (8 letters → 8 letters), and - exactly as with GENERALS → DFGPEVAT - every shifted letter must stay in the same left-to-right position as the letter it replaces. A common trap is to work out the right set of shifted letters but then write them down in the wrong order.

Hence, CHEMICAL is coded as GBOGGMTI.