Genetic disorders result from errors in the DNA of our body cells. Hormonal disorders (for e.g. excessive growth, appearance of facial hair in females, etc) are the results of imbalanced secretion of hormones produced within the body. Similarly, if any body organ malfunctions, i.e. it does not function in proper order, then it is an internal cause. But if there is malnutrition, then the cause is purely external and not within our body. We should remember that cause may be external or internal, but the effect is seen on the general health of our body.

During any accident, wounds occur and they are exposed to air and soil. The air and soil may contain tetanus-causing microbes. Hence, the person is immediately given anti-tetanus injection. 

Pneumonia spreads through air. It is an inflammatory condition of the lung affecting primarily the microscopic air sacs known as alveoli. 

Haemophilia is a disease in which the blood does not clot whenever there is a wound/injury and it is a genetic disorder. It is not caused or spread by infectious agents. Thus, it is a non-infectious disease. Cholera, typhoid and malaria are caused due to microorganisms, which cause infection or disease in the digestive system, immune system and blood (also liver), respectively.

Penicillin blocks the bacterial processes that build the cell wall.

DDT is an insecticide (“insect” + “cidal” – killing). It is used to kill a variety of insects and pests, particularly mosquitoes. It should be noted here that though DDT is useful but at the same time, it is a pollutant and hence, its use must be limited. Apart from DDT, all other options given here are vaccines and hence, they cannot be used to kill mosquitoes because their function is to give immunity inside our body. BCG is a vaccine against TB; ATS is Anti Tetanus Serum and DPT is a triple vaccine against diphtheria, pertusis and typhoid.

Tuberculosis is a chronic disease as it can last for a long time, even as much as a lifetime.

SARS is a respiratory disease caused by a virus. Symptoms usually occur about 2 to 10 days after coming in contact with the virus.

Edward Jenner created the vaccine for smallpox two centuries ago.

Penicillin is an antibiotic obtained from the fungus ‘Penicillium notatum’ and it works against bacteria. Quinine and chloroquine are drugs that are used to treat malaria. Anti-tetanus serum is a vaccine used to prevent tetanus.

Hepatitis is the swelling and inflammation of the liver, most commonly caused by a viral infection. It may lead to liver damage, liver failure or even liver cancer.

An active immune system recruits many cells to the affected tissue to kill off the disease-causing microbes. This recruitment process is called inflammation.

Junk food is not good for health.

This is the correct option as this is a characteristic of communicable diseases.

Pellagra is a vitamin deficiency disease caused by a chronic lack of niacin (vitamin B₃).