Which of the following factors affect human health? (i) Infections (ii) Silent mutation (iii) Lifestyle (iv) Genetic disorders

The correct option is C i, iii and iv
Infection occurs when viruses, bacteria, or other microbes enter your body and begin to multiply. The pathogen rapidly destroys the cells of the host, which adversely affect the immune system and cause infections.

Lifestyle choices affect cardiovascular, psychological, nutritional, skeletal and neurological health. A variety of lifestyle or health-related habits (behavioural factors) can have a major impact on a person's health which includes smoking, alcohol, poor diet leading to obesity or malnutrition, lack of physical exercise, sexual behaviour and problems resulting from drug-taking.

A genetic disorder is caused by an altered or faulty gene or set of genes. These disorders can be found to affect any part of the body, including the brain and the muscles.

Silent mutations are mutations in DNA that do not significantly alter the phenotype of the organism in which they occur, therefore does not affect human.

Therefore, out of the options, only i, iii and iv affects human health.