**Core Concept**
Nitroglycerine (NTG) is a vasodilator used to manage angina pectoris, and its dosage is calculated based on the desired plasma concentration. To achieve a specific rate of infusion, the volume of the solution and the concentration of NTG must be taken into account.

**Why the Correct Answer is Right**
First, we need to calculate the total amount of NTG required for the infusion. Since the patient needs 10 mcg/min of NTG and the infusion will last for 500 ml, we can calculate the total dose as follows: (10 mcg/min) x (500 ml) = 5000 mcg or 5 mg. Given that one ampoule contains 5 mg/ml, we can confirm that this amount of NTG is indeed contained in the 500 ml solution.

Next, we need to calculate the rate of infusion. Since the patient needs 10 mcg/min of NTG, we can calculate the rate as follows: (5 mg) / (500 ml) = 10 mcg/ml. To convert this rate to drops/min, we need to consider that 1 micro drip = 60 drops/ml. Therefore, the rate of infusion is (10 mcg/ml) x (60 drops/ml) / (10 mcg/min) = 60 drops/min / 5 = 12 drops/min.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because it is 2 drops/min higher than the correct answer. To get the correct answer, we need to divide the total number of drops by 5 (since 60 drops/min is 12 x 5).

**Option C:** This option is incorrect because it is 3 drops/min higher than the correct answer. To get the correct answer, we need to divide the total number of drops by 5 (since 60 drops/min is 12 x 5).

**Option D:** This option is incorrect because it is 4 drops/min higher than the correct answer. To get the correct answer, we need to divide the total number of drops by 5 (since 60 drops/min is 12 x 5).

**Clinical Pearl / High-Yield Fact**
When calculating the rate of infusion for medications like nitroglycerine, it's essential to consider the concentration of the medication, the total volume of the solution, and the desired plasma concentration. This requires careful attention to detail and a clear understanding of the medication's pharmacokinetics.

**✓ Correct Answer: A. 12 drops/min**