Explanation

The algebraic expression in the stem could not be recovered; only the options (-1/2, 0, 1/2, 1) survive. The stored key is C (1/2) while the published coaching key (PW, CDS 2 2025 Set A) says A (-1/2). With the stem missing, neither can be verified from first principles, so the stored key is kept. Note: key disputed - independent verification inconclusive.