**Core Concept**
Disulphiram is a medication used to treat chronic alcoholism by producing an unpleasant reaction when alcohol is consumed. This reaction is a result of the accumulation of acetaldehyde, a toxic byproduct of alcohol metabolism.

**Why the Correct Answer is Right**
Disulphiram acts by competitively inhibiting aldehyde dehydrogenase (ALDH), an enzyme responsible for converting acetaldehyde to acetate in the liver. The accumulation of acetaldehyde leads to symptoms such as flushing, nausea, and vomiting, making it unpleasant for the patient to consume alcohol. This mechanism is crucial for the therapeutic effect of disulphiram.

**Why Each Wrong Option is Incorrect**
**Option A:** Alcohol dehydrogenase is the enzyme responsible for converting ethanol to acetaldehyde, but disulphiram does not inhibit this enzyme.
**Option C:** Alcohol carboxylase is not a recognized enzyme involved in alcohol metabolism, and disulphiram does not act on this enzyme.
**Option D:** Aldyhyde carboxylase is not a recognized enzyme involved in alcohol metabolism, and disulphiram does not act on this enzyme.

**Clinical Pearl / High-Yield Fact**
Disulphiram can cause a disulfiram-ethanol reaction, which is characterized by symptoms such as flushing, nausea, and vomiting. This reaction can occur even with small amounts of alcohol, making it a potent deterrent for individuals with a history of alcoholism.

✓ Correct Answer: B. Aldehyde dehydrogenase