Akshay went on an adventurous trip with his friends. He went climbing sky diving and underground water diving. He observed that while all the activities were pleasant during water diving, he and his friends felt nauseous and had breathing difficulties. He was aware of same thing happening to his friends a few year back as he was mountain climbing.
(a) Can you suggest a reason behind all the symptoms faced by Akshay and his friends?
(b) How can one recover from this situation?
(c) Give two more special situations where - same symptoms can develop?
(d) If we suffer from breathing problems in deep water. How do plants and animals living in water cope?
(e) Have you observed any good values in Akshay?

Write a few sentences for an imaginary situation if any of the following gases disappear from the atmosphere.
(a) Oxygen (b) Nitrogen (c) Carbon dioxide

Explain the following observations briefly.
(a) A firki does not rotate in a closed area.
(b) The arrow of weather cock points towards a particular direction at a particular moment.
(c) An empty glass in fact is not empty.
(d) Breathing through mouth may harm you.

Humans and animals use oxygen for respiration and plants require carbon dioxide for photosynthesis. How are these two processes related?

Explain what makes the carbon dioxide gas present in air necessary for all in the atmosphere.

Ravi visited his grandmother's home. All rooms were locked and lights were off. Ravi came into a dark room and started finding a light switch. When he came across a hole in a dark curtain. He saw that through the passing beam of light, tiny particles were moving in the room. He asked questions pertaining to this observation to his teacher.
(a) What has Ravi actually observed in the room?
(b) We breathe air regularly so how do we prevent these particles from entering our body? From where does these dust particles come?
(c) Does breathing through mouth a good practice?
(d) Do you observe any good values in Ravi?

Paheli kept some water in a beaker for heating. She observed that tiny bubbles appeared before the water started to boil. She boiled the water for about 5 min and filled it in a bottle upto the brim and kept the bottle airtight till cooled down to room temperature.
(a) Why did the tiny bubbles appeared?
(b) Do you think tiny bubbles will appear on heating the water taken out from the bottle? Justify your answer.

Air present in atmosphere will be defined as what? Name the major constituents of air. Give their volume proportions in air.

How can you say that air contains dust particles?

Give an experiment to show that one-fifth of air is oxygen.