Select the options which is/are incorrect statement(s) with respect to T-lymphocytes in the human body.

(i) They are a type of white blood cells.

(ii) They are produced in bone marrow.

(iii) They remain active at all times in the body.

(iv) They mature in the bone marrow.

The correct options are (iii) only and (iii) and (iv) only.

To understand why these options are selected as the incorrect statements, let us analyze each of the given statements about T-lymphocytes step-by-step:

Statement (i): "They are a type of white blood cells."
This statement is correct. Lymphocytes (both T-cells and B-cells) are a major type of white blood cell (leukocyte) responsible for the body's immune response.

Statement (ii): "They are produced in bone marrow."
This statement is correct. All blood cells, including T-lymphocytes, originate and are produced in the red bone marrow through a process called hematopoiesis.

Statement (iii): "They remain active at all times in the body."
This statement is incorrect. In a healthy body, T-lymphocytes circulate in an inactive or naive state. They only become active when they encounter a specific antigen presented to them by antigen-presenting cells (APCs) during an infection. Keeping them active at all times would cause autoimmune damage and waste energy.

Statement (iv): "They mature in the bone marrow."
This statement is incorrect. While T-lymphocytes are produced in the bone marrow, they migrate to the thymus gland to undergo maturation and differentiation (which is why they are named "T" lymphocytes). B-lymphocytes, on the other hand, mature in the bone marrow.

Thus, both statement (iii) and statement (iv) are incorrect. Depending on the test evaluation criteria, the options (iii) only and (iii) and (iv) only are the correct choices representing the incorrect statements.