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.

Let us analyze each statement to understand why these options identify the incorrect statements regarding T-lymphocytes in the human body:

Statement (i): They are a type of white blood cells.
This statement is correct. T-lymphocytes (or T cells) are a major type of lymphocytes, which are a subtype of white blood cells (leukocytes) essential for the adaptive immune system.

Statement (ii): They are produced in bone marrow.
This statement is correct. Like all blood cells, T-lymphocytes originate from hematopoietic stem cells in the bone marrow.

Statement (iii): They remain active at all times in the body.
This statement is incorrect. T-lymphocytes do not remain active at all times. They circulate in an inactive (naive) state until they encounter a specific antigen presented by antigen-presenting cells. Once the pathogen is cleared, most active T cells undergo apoptosis, leaving behind a small population of memory T cells that revert to an inactive state until re-exposure.

Statement (iv): They mature in the bone marrow.
This statement is incorrect. Although T-lymphocytes are produced in the bone marrow, they migrate to the thymus gland to undergo maturation and selection (hence the name "T"-lymphocytes for thymus-derived).

Since statements (iii) and (iv) are incorrect, the options that correctly identify the incorrect statements are (iii) only (focusing on the physiological activity state) and (iii) and (iv) only (fully identifying both incorrect statements).