The correct option is
C health is a state of complete physical, mental and social well being
There is a feeling that if you are not ill, you are healthy. But health is not just the balance of body and mind. According to the World Health Organisation(WHO), health is a state of complete physical, mental and social well being and not merely the absence of a disease. So option (c) is correct.
If we consider physiology then balance simply means the balance of ionic concentration, hormone concentration etc., but if the same person is not able to socialise with the members of the community, then he is not healthy.
Mental fitness is an important aspect of health. A person needs to think and analyse things properly to succeed in life. Physical fitness is another important factor that affects health. A person can perform his duties in a proper way in the society if he is physically fit.
Health is not limited to a smiling face or physical fitness alone. For example, people who have Down’s syndrome always have a smiling face. A person is a bodybuilder but has less sperm count, then he is not considered healthy. People normally notice the outward appearance, but it is not necessary that a person with strong musculature and physique is healthy. Many of the mentally ill people look physically fit. So option (a), (b) and (d) are wrong.