Key idea: ceric ammonium nitrate (CAN) test

Ceric ammonium nitrate gives a positive test mainly with alcoholic $-OH$ groups (especially aliphatic alcohols), producing a red/orange coloration.

It is not the usual positive test for:

• phenolic $-OH$
• carboxylic acid $-OH$
• enolic $-OH$ (generally not considered the characteristic positive case here)

Interpretation of the product $P$

In this standard question type, the product $P$ contains several kinds of oxygen-bearing groups labeled as $(a), (b), (c), (d)$, and we are asked which labeled $-OH$ group is responsible for the positive CAN test.

Since CAN test is given by an alcoholic hydroxyl group, among the labeled groups the one corresponding to an ordinary alcohol is $(b)$ only.

Checking options

• A: $(b)$ only $\rightarrow$ matches alcoholic $-OH$
• B: $(b)$ and $(d)$ $\rightarrow$ incorrect if $(d)$ is not an alcohol-type $-OH$
• C: $(c)$ and $(d)$ $\rightarrow$ incorrect
• D: $(d)$ only $\rightarrow$ incorrect

Final conclusion

The positive ceric ammonium nitrate test is due to the presence of $(b)$ only.