A non-infectious, unnatural and unusual reaction to a substance or condition is

The correct option is D Allergy

Immunity ;
The ability of the body to protect itself against all types of foreign bodies or antigens (e.g, bacteria, viruses, toxic substances, etc) which enter the body is called immunity.

Allergy :
Allergy or hypersensitivity is the unusual and unnaturally heightened or exaggerated immunological response that is manifested by the body against certain antigens in the environment which are specifically called allergens. It is a non-infectious disorder.

Infection :
Infection is the entry and multiplication of pathogens within the body.

Toxin :
Toxin is a poisonous chemical that is released by invading pathogens and has toxic effects on the host body. It is capable of inducing antibody production in the host’s body.

Final answer :
(B) Allergy