Identify the reaction sequence

This standard question corresponds to the reaction of ethanol/acetaldehyde under exhaustive iodination in alkali, followed by further reaction of the carboxylate formed.

The key reaction involved is the iodoform reaction:

$RCOCH_3 \xrightarrow[I_2]{\text{alkali}} RCOO^- + CHI_3$

In particular, for ethanal:

$CH_3CHO \xrightarrow[I_2/\text{alkali}]{} HCOO^- + CHI_3$

and for ethanol, since ethanol is first oxidized to ethanal under these conditions, it also gives the same products.

Determine compound B

The yellow precipitate formed in the iodoform reaction is iodoform, whose formula is:

$CHI_3$

Hence,

$B = CHI_3$

Determine compound C

Along with iodoform, the remaining fragment from ethanal becomes formate salt in alkaline medium:

$HCOO^-K^+ = HCOOK$

So,

$C = HCOOK$

Match with options

The pair $(B, C)$ is:

$CHI_3,\ HCOOK$

This matches Option C.

Compare with stored answer

Stored correct answer is D: $CHI_3,\ CH_3COOK$.

But the iodoform reaction gives a carboxylate with one carbon less in the methyl ketone fragment accounting, and for ethanal/ethanol the carboxylate formed is formate, not acetate.

Therefore, the stored answer appears incorrect.