**Core Concept**
Propranolol, a non-selective beta-blocker, is used to manage various cardiovascular and neurological conditions. Its effectiveness in these conditions relies on its ability to block beta-adrenergic receptors, thereby reducing sympathetic tone and cardiac output.

**Why the Correct Answer is Right**
Propranolol is not particularly useful for Parkinsonian tremor because it can worsen tremors in some patients. This is due to its ability to block beta-2 receptors in the brain, which can lead to increased dopamine release and exacerbate tremors. Propranolol's use in Parkinsonian tremor is generally contraindicated, and other medications like primidone or propranolol's selective beta-1 blocking counterpart, atenolol, may be considered.

**Why Each Wrong Option is Incorrect**
**Option A:** Atrial flutter is a type of supraventricular tachycardia (SVT) that can be effectively managed with propranolol, which helps to slow the heart rate and prevent further episodes. Propranolol's beta-blocking action helps to decrease the automaticity of the sinoatrial node and the atrioventricular node.
**Option C:** Thyrotoxicosis, a condition caused by an overactive thyroid gland, can be treated with propranolol to manage symptoms such as tachycardia and tremors. Propranolol's beta-blocking action helps to counteract the excess thyroid hormones and their effects on the heart and nervous system.
**Option D:** Hypertrophic obstructive cardiomyopathy (HOCM) is a condition characterized by thickening of the heart muscle, which can lead to obstruction of blood flow. Propranolol is useful in managing HOCM by reducing the heart rate and contractility, thereby decreasing the obstruction and improving symptoms.

**Clinical Pearl / High-Yield Fact**
When using beta-blockers like propranolol, it's essential to consider the specific type of tremor you're treating. Beta-blockers can worsen certain types of tremors, such as Parkinsonian tremor, while improving others, like essential tremor.

**✓ Correct Answer: B. Parkinsonian tremor**