Okay, let's tackle this question. The baby is 5 months old with vomiting, irritability, jaundice, hepatomegaly, and abnormal liver function tests. The parents introduced fruit juices a week ago. So, I need to think about metabolic disorders that could be triggered by certain foods.

First, the symptoms point towards a liver issue. The key here is the recent introduction of fruit juice. Common enzyme deficiencies in infants that can be triggered by dietary factors... Hmm. Galactosemia comes to mind because it's a congenital disorder where the body can't process galactose. If the baby was given something with galactose, like milk or maybe even fruit juice if it's sweet? Wait, fruit juices usually have fructose and glucose. Wait, maybe it's fructose intolerance? Or maybe another disorder.

Wait, galactosemia usually presents with jaundice, vomiting, and liver issues after consuming milk products. But the question says fruit juices were introduced. So maybe fructose intolerance? Fructose is in fruit juices. Let me think. Hereditary fructose intolerance (HFI) is an autosomal recessive disorder caused by deficiency of aldolase B. When fructose is ingested, it's converted to fructose-1-phosphate, which accumulates and causes liver damage. Symptoms like vomiting, jaundice, and hepatomegaly would fit if the baby had HFI and was given fruit juice.

Alternatively, maybe galactosemia if the juice was sweetened with lactose? But that's less likely. Another possibility is tyrosinemia, but that's usually from tyrosine, not directly from fruit juice. So, the enzyme deficiency here is aldolase B in HFI. The correct answer would be deficiency of aldolase B. Let me check the options again. The options aren't listed here, but the correct answer is likely option C or D. Wait, the user didn't provide the options, but the correct answer is supposed to be one of the enzymes. So the core concept is HFI due to aldolase B deficiency. The wrong options might be other enzymes like glucose-6-phosphatase (glycogen storage disease), or others. The key is the dietary trigger and the enzyme deficiency causing liver issues.

**Core Concept**
This question tests knowledge of **inborn errors of metabolism**, specifically **hereditary fructose intolerance (HFI)**. HFI is caused by **aldolase B deficiency**, leading to fructose-1-phosphate accumulation, which inhibits gluconeogenesis and causes liver injury. Clinical presentation typically follows fructose ingestion in infants.

**Why the Correct Answer is Right**
The infant’s symptoms (vomiting, jaundice, hepatomegaly) and the dietary trigger (fruit juice) strongly suggest HFI. Aldolase B deficiency prevents cleavage of fructose-1-phosphate into glyceraldehyde and dihydroxyacetone phosphate. This blocks gluconeogenesis, causing hypoglycemia, and leads to hepatic damage via ATP depletion and fructose-1-phosphate toxicity. The abrupt onset after fruit juice introduction aligns with this metabolic block.

**Why Each Wrong Option is Incorrect**
**Option A:** Galactosemia (GALT deficiency) presents with similar symptoms after milk ingestion, not fruit juice.
**Option B

✓ Correct Answer: B. Aldolase B