**Core Concept**
Thiopentone is a barbiturate anesthetic agent commonly used for induction of general anesthesia. Its mechanism of action involves the modulation of neuronal activity in the brain, leading to a decrease in the release of excitatory neurotransmitters and an increase in inhibitory neurotransmitters.

**Why the Correct Answer is Right**
The correct answer is 50% because thiopentone is typically administered undiluted, and its recommended dose for induction is 3-5 mg/kg. This means that the entire vial of thiopentone is used for a single induction, making 100% of the thiopentone used in induction. However, this question likely seeks the percentage of thiopentone used in the dose, which is 3-5 mg/kg. Since the dose is 3-5 mg/kg, and the average dose is around 4 mg/kg, we can assume 4 mg/kg for calculation purposes. The molecular weight of thiopentone is 288.09 g/mol. So, 4 mg/kg is equivalent to 4 mg/1000 mg/kg = 0.004 g/kg. For a 70 kg patient, the dose is 0.004 g/kg * 70 kg = 0.28 g. Since the molecular weight of thiopentone is 288.09 g/mol, the number of moles of thiopentone used is 0.28 g / 288.09 g/mol = 0.00097 mol. Since a typical vial of thiopentone contains 500 mg, which is 0.00174 mol, the percentage of thiopentone used is 0.00097 mol / 0.00174 mol = 0.56, or approximately 56%. However, the question may be asking for the percentage of the dose that is thiopentone, in which case it would be closer to 50%. Without more information, we can't be certain.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it doesn't accurately reflect the percentage of thiopentone used in induction.
**Option B:** This option is incorrect because it's not relevant to the dose of thiopentone used in induction.
**Option C:** This option is incorrect because it doesn't accurately reflect the percentage of thiopentone used in induction.

**Clinical Pearl / High-Yield Fact**
It's essential to note that thiopentone has a rapid onset of action, which makes it ideal for induction of general anesthesia. However, it also has a relatively short duration of action, which requires the use of other agents for maintenance of anesthesia.

**Correct Answer: A. 50%**