Correct Answer: A

Rationale: The correct answer is Chlorine (Cl). The atomic number of an element corresponds to the number of protons in its nucleus. Chlorine has an atomic number of 17, indicating it has 17 protons. Therefore, the element with atomic number 17 is Chlorine (Cl). Choice B, Nitrogen (N), has an atomic number of 7, Choice C, Sodium (Na), has an atomic number of 11, and Choice D, Fluorine (F), has an atomic number of 9. These elements do not match the atomic number 17, making them incorrect choices.

Correct Answer: B

Rationale: The pH scale measures the acidity or basicity of a solution. A pH of 7 is considered neutral, indicating that the concentration of hydrogen ions (H+) is equal to the concentration of hydroxide ions (OH-) in the solution. A pH ranging from 0 to 6.9 signifies acidity, while a pH from 7.1 to 14 signifies alkalinity. Therefore, a neutral solution has a pH value of 7. Choice A (0) represents a highly acidic solution, Choices C (14) and D (-7) are outside the valid pH range and do not correspond to a neutral solution.

Correct Answer: B

Rationale: The primary function of the lymphatic system is to remove excess fluids, waste products, and toxins from tissues. It maintains fluid balance and supports the immune system by transporting lymph, which contains white blood cells, throughout the body. Choice A is incorrect as nutrient transport is primarily handled by the circulatory system. Choice C is incorrect because red blood cells are produced in the bone marrow, not the lymphatic system. Choice D is incorrect as the regulation of body temperature is mainly controlled by the endocrine system and thermoregulatory mechanisms in the body. Therefore, the correct answer is B.

Correct Answer: C

Rationale: During the flight of the object, the only force that acts horizontally on the object is air resistance. Air resistance opposes the motion of the object through the air and acts in the direction opposite to the object's velocity. Gravitational force acts vertically downward, influencing the object's weight and vertical motion. The normal force from the ground acts perpendicular to the ground to support the object's weight. The force of throwing initially imparts velocity to the object at an angle, but it does not act horizontally throughout the flight.

Correct Answer: C

Rationale: A commensal relationship is a type of symbiotic relationship in which one organism benefits, while the other is neither harmed nor benefited. In this case, E. coli living in the gut is an example of a commensal relationship because it can benefit from the environment in the gut without causing harm to the human host. Option A, Salmonella causing food poisoning, is an example of a pathogenic relationship where the microorganism causes harm to the host. Option B, Staphylococcus aureus causing skin infections, is also an example of a pathogenic relationship where the microorganism causes harm to the host. Option D, Rabies virus causing neurological disease, is another example of a pathogenic relationship where the microorganism causes harm to the host.