Among the following statements, which one is not correct?
A. Aspirin is both an analgesic and an antipyretic
B. Ampicillin is a natural antibiotic
C. Sulphadiazene is a synthetic antibacterial
D. Some disinfectants can be used as antiseptics at low concentration

Hint: Chemical substances used in the treatment of diseases and for reducing pain and various other purposes are called drugs or medicines. There are various classifications in drugs; which include analgesics, antipyretic, antibiotic, antibacterial, antiseptic etc. Natural antibiotics are substances which are naturally present in the environment in some kind of microorganisms or plants.

Complete solution:
Let us analyse each point one by one here;
Aspirin which is acetylsalicylic acid is a salicylate drug which is used as an analgesic to treat pains and aches as well as an antipyretic to reduce fever. So, this statement is correct. Salicylic acid, aspirin 's principal metabolite, is an essential part of the metabolism of humans and livestock.
Antibiotics are chemical substances which are produced wholly or partly by chemical synthesis which inhibits or destroys microorganisms by intervening in their metabolic processes. Ampicillin is a penicillin beta-lactam antibiotic used in the treatment of susceptible, usually gram-positive, organisms causing bacterial infections. Ampicillin is a semi-synthetic penicillin derivative that functions as a broad-spectrum oral antibiotic. This is not a natural antibiotic so this statement is not correct.
Sulfadiazine is a synthetic analogue of pyrimidinyl sulfonamide, a short-acting bacteriostatic sulfadiazine that, by competing with para amino benzoic acid, inhibits bacterial folic acid synthesis. Sulfadiazine is an antibacterial sulfonamide agent used to treat mild to moderate infections caused by sensitive organisms. Hence, this statement is correct.
To kill any microorganisms living on the surface of the body, antiseptics are used on living organisms, such as human skin. Disinfectants are used on non-living things to kill the microorganisms living on that inanimate surface, such as countertops and handrails. Phenol is an example of a disinfectant which can be used as an antiseptic in low concentration. So, this statement is also correct.
From the above explanations, it is clear that option B is the correct answer for this question.

Note: Ampicillin's bactericidal activity results from the inhibition of cell wall synthesis and is mediated by the binding of Ampicillin to penicillin binding proteins. It was one of the first semi-synthetic antibiotics developed.