Question

Assertion (A): The function of kidneys is to remove the poisonous substances urea, other waste salts and excess water from the blood and excrete them in the form of a yellowish liquid called urine.

Reason (R): 1 mL of very dilute starch solution (1% starch solution) is taken in a test-tube and 1 mL of saliva is added to it. After keeping this mixture for half an hour, a few drops of dilute iodine solution are added to the test-tube. A blue-black colour is produced.

Options

• Both A and R are true and R is correct explanation of the assertion.

• Both A and R are true but R is not the correct explanation of the assertion.

• A is true but R is false.

• A is false but R is true.

Answer 1

A is true but R is false.

Explanation:

• Assertion (A) is true: Kidneys remove urea, excess salts, and water from the blood and excrete them as urine.
• Reason (R) is false: Saliva digests starch into sugars. Therefore, after half an hour, iodine does not produce a blue-black colour because the starch has been digested.