.............. has a tremendous effect on the health of an individual, specially in children.

The correct option is D Malnutrition

1. Malnutrition is a condition that results from eating a diet in which one or more nutrients are either not enough or are too much such that the diet causes health problems.
2. If an individual is not provided with enough nutrients, they are called undernutrition or undernourishment while too much is called overnutrition.
3. If undernutrition occurs during pregnancy, or before two years of age, it may result in permanent problems with physical and mental development.
4. Symptoms that include: a short height, thin body, very poor energy levels, and swollen legs and abdomen. Hence, malnutrition has a tremendous effect on the health of an individual, especially in children.
   

So, the correct answer is 'malnutrition'.