NCERT Solutions For Class 9 Science Chapter 13
Why do we Fall ill?

c. You are most likely to fall sick when you will be in the company of your friend who is suffering from measles.

Measles is a highly contagious disease that spreads through droplets from the nose or mouth of the infected person. Therefore, if your friend is suffering from measles, you should stay away from him/her to protect yourself from the disease.

The three most common diseases are:

1. Malaria
2. Jaundice
3. Typhoid

Steps that should be taken by the local authorities to bring down the incidence of these diseases:

1. Avoid collection of  stagnant water in the surroundings to prevent mosquitoes from breeding
2. Ensuring the supply of clean drinking water
3. Managing the proper disposal of sewage and waste to check the breeding ground of germs or causative agents of various diseases

A doctor/nurse/health-workers, generally, take the following precautions:

1. They wear a mask while treating the infected person.
2. They keep themselves covered while moving around an infected area. 
3. They eat healthy and nutritious food and drink lots of clean water.
4. They give importance to personal and community hygiene.

Frequency of falling ill varies from person to person. It depends on personal factors such as the immunity of a person and environmental factors such as cleanliness in the surrounding in which he/she is living. Some of the common diseases from which generally children get affected are cold, cough, fever, stomach infection, dengue, malaria, typhoid, etc.

1. To avoid most of the above mentioned illnesses a person should have healthy eating habits. He/she should eat balanced diet that would help in his/her growth and development. A person should include lots of fruits in his diet as fruits boost up our immune system and provide minerals and vitamins that protect us from many diseases. 
2. To avoid the spread of diseases like dengue, malaria, etc, one has to keep his surroundings clean so that the germs causing these diseases would not get a chance to grow and multiply. By doing so one can stop the diseases like dengue, malaria, typhoid, etc.

c. A person is most likely to fall sick when she is on a four day fast after recovering from malaria and is taking care of someone suffering from chicken pox.

Fasting just after the recovery from malaria would definitely weaken the immune system of the person and would not even help her to fight with any infection if she comes in contact with it. Under these conditions, if she takes care of someone who is suffering from chicken pox, she is more likely to get infected from chicken pox and will fall sick.

1. Following behavioural changes in the baby would help us to find out that the baby is sick:

1. Constant crying of the baby,
2. Avoiding his/her meal
3. Mood swings in the baby

2. The sickness in a baby can be identified by the following symptoms or indications:

1. vomiting
2. fever
3. loose motions
4. dullness in activity