Correct Answer: B

Rationale: The correct answer is B: Melatonin. Melatonin, produced by the pineal gland, is the hormone that regulates the sleep-wake cycle. It helps signal to the body when it's time to sleep and wake up, playing a crucial role in maintaining a healthy sleep pattern. Choice A, Cortisol, is known as the stress hormone and plays a role in the body's response to stress, not specifically in regulating the sleep-wake cycle. Choice C, Thyroxine, is a hormone produced by the thyroid gland that regulates metabolism, not the sleep-wake cycle. Choice D, Insulin, is a hormone produced by the pancreas that regulates blood sugar levels, not the sleep-wake cycle.

Correct Answer: B

Rationale: The question inquires about the brain region responsible for voluntary muscle movements. The correct answer is the Cerebrum. The cerebrum is the main part of the brain involved in voluntary muscle control and motor coordination. The Medulla oblongata is primarily responsible for regulating vital functions like breathing and heart rate, not voluntary muscle movements. The Hypothalamus plays a role in regulating body temperature, thirst, hunger, and other homeostatic processes. The Thalamus serves as a relay station for sensory information but is not directly responsible for voluntary muscle movements.

Correct Answer: B

Rationale: The correct answer is B: Elbow joint. A hinge joint allows movement primarily in one plane, enabling bending and straightening actions. The elbow joint specifically functions as a hinge joint, facilitating the bending and straightening of the arm. The other options, such as the hip joint (A), shoulder joint (C), and knee joint (D), are not examples of hinge joints as they allow movement in multiple planes with more complex motions.

Correct Answer: B

Rationale: The correct answer is B: Adhesion. Water's polarity allows it to dissolve many substances due to its ability to adhere to and interact with other molecules, making it an effective solvent. Cohesion refers to water molecules sticking together, molarity is a measure of concentration, and dilution refers to the process of reducing the concentration of a solute in a solution, none of which directly relate to water's role as a universal solvent.

Correct Answer: C

Rationale: The parietal lobe is responsible for sensation, perception, and spatial reasoning. It plays a crucial role in processing sensory information, assisting in spatial orientation, and integrating various sensory inputs to create a comprehensive perception of the surrounding environment. The frontal lobe, although important for higher cognitive functions and motor skills, is not primarily responsible for sensation, perception, or spatial reasoning. The occipital lobe is mainly involved in visual processing, and the temporal lobe is primarily associated with auditory processing, memory, and emotions, making them incorrect choices for this question.