The primary immune response is:

The correct answer is Option (1) → Low intensity and pathogen specific

Acquired immunity is pathogen specific and has memory. The first time the body meets a pathogen, it gives a primary response, which is of low intensity. The next time it meets the same pathogen, it gives a much stronger secondary (anamnestic) response, because it remembers the first encounter.

Option (1) Low intensity and pathogen specific — Correct. The primary response is the first, weak response to a pathogen. Being a part of acquired immunity, it is directed against that particular pathogen.

Option (2) High intensity and pathogen specific — Incorrect. High intensity belongs to the secondary response, which comes on a later encounter with the same pathogen.

Option (3) Low intensity and non-specific — Incorrect. The intensity is right, but the response is not non-specific. Non-specific defence is innate immunity (skin, stomach acid, phagocytes and interferons), which acts against all invaders alike.

Option (4) High intensity and non-specific — Incorrect. Both parts are wrong: the primary response is of low intensity, and it is specific to the pathogen.

NCERT Extract:
Acquired Immunity – “Acquired immunity, on the other hand is pathogen specific. It is characterised by memory. This means when our body encounters a pathogen for the first time it produces a response called primary response which is of low intensity. Subsequent encounter with the same pathogen elicits a highly intensified secondary or anamnestic response. This is ascribed to the fact that our body appears to have memory of the first encounter.”