Okay, let's tackle this question. The question is about a pregnant woman with thyrotoxicosis needing surgery, and what medication should be given to reduce the thyroid size and vascularity before surgery.

First, I need to recall the standard preoperative management for hyperthyroidism. The main goal before surgery is to decrease the size and vascularity of the thyroid gland to make the surgery safer. The usual approach involves antithyroid drugs and iodine solutions.

Thyrotoxicosis in pregnancy is tricky because of the need to balance maternal and fetal health. Antithyroid medications like propylthiouracil (PTU) or methimazole are used, but the question is about pre-surgical preparation. I remember that potassium iodide or saturated solution of potassium iodide (SSKI) is given for this purpose. These iodine solutions help in reducing the vascularity and size of the thyroid gland. They work by inhibiting the release of thyroid hormones and decreasing blood flow to the gland.

Now, looking at the options, even though they aren't listed, the correct answer is likely to be an iodine solution. Common distractors might include other antithyroid drugs like PTU or methimazole, which are used for long-term management but not for pre-surgical preparation. Another possible wrong option could be a beta-blocker like propranolol, which is used to control symptoms but doesn't reduce thyroid size. Radioactive iodine is contraindicated in pregnancy, so that's another distractor.

The core concept here is the use of iodine solutions in preoperative management. The iodine causes a decrease in thyroid hormone release and vasoconstriction, leading to a smaller, less vascular gland. Other drugs don't address the vascularity as effectively. The clinical pearl is that iodine solutions are the mainstay before surgery, and beta-blockers are for symptom control. So the correct answer should be potassium iodide.

**Core Concept**
Preoperative management of thyrotoxicosis requires decreasing thyroid size and vascularity to minimize surgical risks. **Potassium iodide (KI)** or **saturated solution of potassium iodide (SSKI)** is the standard preoperative preparation due to its vasoconstrictive and antithyroid effects.

**Why the Correct Answer is Right**
Potassium iodide reduces thyroid vascularity by inhibiting the release of thyroid hormones and decreasing capillary permeability in the gland. It also induces a transient decrease in thyroid hormone synthesis. This effect, known as the **Wolff-Chaikoff effect**, is critical for achieving a "quiet gland" before surgery, lowering hemorrhage risk and surgical difficulty.

**Why Each Wrong Option is Incorrect**
**Option A:** Beta-blockers (e.g., propranolol) control symptoms like tachycardia but do not reduce thyroid size or vascularity.
**Option B:** Methimazole/propylthiouracil (PTU) inhibit hormone synthesis but increase vascularity initially, making surgery riskier if used alone.
**Option C:** Radioactive iodine is contraindicated in pregnancy and not used for preoperative preparation.

**Clinical Pearl / High-Yield Fact**
Remember: **"Iodine shrinks the gland, beta-blockers calm the hand."**

✓ Correct Answer: C. Propylthiouracil