**Core Concept**
The question is testing the understanding of a specific molecule involved in both cataract formation and liver toxicity. This molecule is a nucleotide sugar that plays a crucial role in glycosylation pathways.

**Why the Correct Answer is Right**
The correct answer is a molecule called **UDP-glucose**. UDP-glucose is an initiator of cataract formation in the eye lens due to the accumulation of sugar in the lens, leading to osmotic changes and water influx, resulting in lens opacity. The 1-phosphate derivative of UDP-glucose, **UDP-glucuronic acid**, is a key molecule in the conjugation pathway of bilirubin in the liver, and its accumulation can lead to liver failure.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is not a relevant molecule in the context of cataract formation or liver toxicity.
* **Option B:** This molecule is involved in different biochemical pathways and is not directly related to cataract formation or liver toxicity.
* **Option D:** This molecule is involved in the metabolism of amino acids, but it is not directly related to the described conditions.

**Clinical Pearl / High-Yield Fact**
UDP-glucose is also involved in the biosynthesis of glycogen, and its accumulation can lead to glycogen storage diseases. This highlights the importance of understanding the metabolic pathways of UDP-glucose in various tissues.

**Correct Answer: B. UDP-glucose.