Thionyl chloride on reaction with white phosphorus gives a compound of phosphorus ' C ' which on hydrolysis gives an oxo acid ' O '. The correct statements about C and O are
I. Shape of ' C ' is pyramidal
II. ' O ' is a dibasic acid
III. ' O ' is a monobasic acid
IV. 'C' on reaction with acetic acid gives 'O'

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.