Correct Answer: A

Rationale: The nephron is the correct answer. It is the structural and functional unit of the kidney responsible for filtering blood. The nephron consists of a renal corpuscle (glomerulus and Bowman's capsule) and a renal tubule. Within the nephron, blood is filtered to form urine, which is then carried to the ureter for excretion from the body. Choices B, C, and D are incorrect because the ureter, urethra, and bladder are not involved in the filtration of blood in the kidney. Instead, they are parts of the urinary system responsible for transporting and storing urine.

Correct Answer: A

Rationale: The correct answer is A: 'Number of elements.' In a balanced chemical equation, coefficients represent the ratio of moles of each species involved in the reaction. They indicate the relative number of molecules or formula units of each compound taking part in the reaction. Choice B, 'Ratio of reactants and products,' is incorrect because the coefficients in a balanced equation do not represent the ratio of reactants and products directly, but rather the stoichiometry of the reaction. Choice C, 'Physical state of the substances,' is incorrect because the physical states (solid, liquid, gas, or aqueous) are denoted with symbols next to the chemical formula, not the coefficients. Choice D, 'Rate of the reaction,' is incorrect as coefficients in a balanced equation do not provide information about the rate of the reaction, which is determined by factors like temperature, concentration, and catalysts.

Correct Answer: C

Rationale: Thyroxine, also known as T4, is a hormone produced by the thyroid gland that plays a crucial role in regulating the body's metabolism, growth, and development. It helps control the rate at which the body uses energy, affects protein synthesis, and influences the body's sensitivity to other hormones. Calcitonin (A) is another hormone produced by the thyroid gland, but its primary function is to regulate calcium levels in the blood. Parathyroid hormone (PTH) (B) is produced by the parathyroid glands and is involved in regulating calcium and phosphorus levels in the body. Insulin (D) is a hormone produced by the pancreas that helps regulate blood sugar levels.

Correct Answer: B

Rationale: The correct answer is B: Alveoli. The alveoli are the small air sacs in the lungs where gas exchange occurs. Oxygen from the air we breathe passes into the bloodstream through the alveoli, while carbon dioxide from the bloodstream passes out of the body through the alveoli. Choice A, Bronchi, are the main airways in the lungs and not the site of gas exchange. Choice C, Trachea, refers to the windpipe, which is a different structure than the alveoli. Choice D, Bronchioles, are smaller airways branching off from the bronchi and are not where gas exchange primarily occurs.

Correct Answer: A

Rationale: Elements within the same group share similar electron configurations in their outermost shells, resulting in comparable chemical properties. Helium and Neon both belong to Group 18 (Noble Gases), explaining their similarities. Boron, Carbon, and Oxygen are not in the same group as Helium on the periodic table. Boron is in Group 13, Carbon is in Group 14, and Oxygen is in Group 16, which are different from Helium's Group 18.