Final answer:
The correct answer to the student's question is c) Kidney. The kidneys are crucial for filtering blood, maintaining water balance, and regulating pH levels, whereas the other organs listed have different primary functions, although they might also contribute to excretion in various ways.
Step-by-step explanation:
The organ that is responsible for removing waste products from the blood and assisting in maintaining water and acid-base balance in the body is the kidney. The functions of the kidney include filtering metabolic waste products from the bloodstream, regulating the body's water balance, and maintaining the pH of the body's fluids. Each day, the kidneys filter the entire blood supply numerous times, eliminating waste and excess water in the form of urine. Other excretory organs, such as the liver, spleen, large intestine, skin, and lungs, also play roles in waste elimination and homeostasis, though their primary functions differ from those of the kidneys. It's important to note that the liver is involved in excretion through the production of bile which carries waste products, but its role is not primarily in regulating the water balance and acidity of the body. Thus, the correct answer to the question is c) Kidney, with the other options not primarily fulfilling the functions outlined.