**Core Concept**
Propanolol is a non-selective beta-blocker used in the management of thyrotoxicosis to control symptoms such as tachycardia, tremors, and anxiety. It works by competitively inhibiting the action of endogenous catecholamines on beta-adrenergic receptors in the body. However, its effect on oxygen consumption in patients with thyrotoxicosis is limited.

**Why the Correct Answer is Right**
Propranolol does not affect the increased metabolic rate or oxygen consumption in patients with thyrotoxicosis. This is because the increased oxygen consumption is primarily due to the enhanced metabolic activity of the thyroid hormone, which is not directly influenced by beta-blockade. Propranolol's primary action is on the adrenergic receptors, which are involved in the symptoms of thyrotoxicosis such as tachycardia and tremors.

**Why Each Wrong Option is Incorrect**
**Option A:** Anxiety is controlled by propranolol as it has a central nervous system (CNS) activity that helps in reducing anxiety in patients with thyrotoxicosis.
**Option B:** Tachycardia is controlled by propranolol as it competitively inhibits the action of endogenous catecholamines on beta-1 adrenergic receptors in the heart, leading to a decrease in heart rate.
**Option C:** Tremor is controlled by propranolol as it has a peripheral effect on the skeletal muscles, reducing the tremors associated with thyrotoxicosis.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that propranolol does not affect the long-term outcome of thyrotoxicosis and does not reverse the metabolic abnormalities associated with this condition. Therefore, it should be used in conjunction with other treatments, such as antithyroid medications or radioactive iodine, to manage the condition effectively.

**✓ Correct Answer: D. O 2 consumption**