Which one of the following properties makes labetalol different from nearly all the other β-blockers on the market?

Correct Answer: A

Rationale: The correct answer is A because labetalol is unique among most β-blockers as it also blocks alpha-adrenergic receptors. This dual action results in vasodilation and reduced blood pressure. Choice B is incorrect as labetalol does not cause atropine-like side effects. Choice C is incorrect as labetalol blocks both β1 and β2 receptors. Choice D is also incorrect as labetalol does have some β2 blocking activity, making it not entirely safe for asthmatics.

Correct Answer: A

Rationale: The correct answer is A because an endothermic reaction absorbs thermal energy from the surroundings to proceed. In an endothermic reaction, the products have higher potential energy than the reactants, requiring energy input. Choice B is incorrect as endothermic reactions do not transfer thermal energy to the surroundings. Choices C and D are incorrect as they describe exothermic reactions, where thermal energy is released to the surroundings.

Correct Answer: B

Rationale: The correct answer is B (green, violet) because green has a lower frequency than violet in the visible light spectrum. Green light has a wavelength longer than violet light, meaning it has lower frequency. This is based on the electromagnetic spectrum where colors are arranged in order of increasing frequency from red (lowest) to violet (highest). Other choices are incorrect because they do not follow the order of increasing frequency as per the visible light spectrum.

Correct Answer: B

Rationale: The correct answer is B: iodine. Iodine is an essential element required for the synthesis of thyroid hormone. Thyroid hormones such as thyroxine (T4) and triiodothyronine (T3) contain iodine atoms. Without sufficient iodine, the thyroid gland cannot produce these hormones, leading to thyroid disorders like hypothyroidism or goiter. Copper (A), sulfur (C), and zinc (D) are not directly involved in the synthesis of thyroid hormone. Copper is important for enzyme function, sulfur is present in amino acids, and zinc is involved in various cellular processes but not specifically in thyroid hormone synthesis.

Correct Answer: A

Rationale: The correct answer is A: damage to the pineal gland. The pineal gland does not regulate ADH secretion; it primarily produces melatonin. Neurosurgery and general anesthesia may disrupt the feedback mechanisms controlling ADH release. Ectopic ADH secretion by pulmonary cancer can lead to excessive ADH production. The key is to identify a situation where ADH hypersecretion is less likely to occur due to the gland's function.