**Core Concept**
The question is testing the ability to recall the composition of Nux vomica seeds, specifically the presence of two alkaloids. Nux vomica seeds are a source of several bioactive compounds, but the question focuses on the two most important alkaloids.

**Why the Correct Answer is Right**
Strychnine is a well-known toxic alkaloid found in Nux vomica seeds, responsible for their potent neurotoxic effects. The other major alkaloid present in Nux vomica seeds is brucine. Brucine has a similar structure to strychnine and also exhibits toxic properties, although its effects are less pronounced. Brucine acts as a competitive antagonist of the glycine receptor, which is involved in the regulation of inhibitory neurotransmission in the central nervous system.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, but if it were a distractor, it would be incorrect because it would not accurately represent the composition of Nux vomica seeds.
* **Option B:** This option is also not provided, but if it were a distractor, it would be incorrect because it would not accurately represent the composition of Nux vomica seeds.
* **Option C:** This option is also not provided, but if it were a distractor, it would be incorrect because it would not accurately represent the composition of Nux vomica seeds.
* **Option D:** This option is also not provided, but if it were a distractor, it would be incorrect because it would not accurately represent the composition of Nux vomica seeds.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that Nux vomica seeds contain two toxic alkaloids, strychnine and brucine, which can cause severe neurotoxic effects if ingested. The toxicity of these alkaloids is due to their ability to disrupt normal neurotransmission in the central nervous system.

**Correct Answer: B. Brucine**