Q23. Why mountaineers carry oxygen cylinders with them, while
climbing high mountains?
carry oxygen cylinders with them, while climbing high mountains because as we
go up higher and higher, level of oxygen decreases.
Q24. Why do you feel suffocated in a closed space after sometime
if a material is burning?
Burning of some material releases smoke and soot which is harmful, thus we feel
suffocated in a closed space, where some material is burning.
Q25. Why does the transparent glass of windows appear hazy if
not wiped off for long time?
contains water vapors and dust particles which stick to transparent glass of
windows. Thus glass of windows appears hazy.
Q26. Why is it not advisable to breathe through our mouth?
It is not advisable to breathe through our mouth because if we do that, harmful
dust particles may enter our body.
Q27. Dia took an open mouth bottle and dips it upside down into
the water. Will the water move inside the bottle? Give a reason to support your
No, water will not move inside the bottle because it was filled completely with
air and there was no space for air to escape.
Q28. When an open mouth bottle is tilted and dipped into water,
bubbles coming out of the bottle was observed. Explain the reason.
the bottle was tilted, the air was able to come out in the form of bubbles, and
water filled up the empty space that the air has occupied.
Q29. How carbon dioxide enters the atmosphere?
Carbon dioxide enters the atmosphere in the following way:
Respiration by plants and animals
Burning of fuel
Q30. List two uses of wind energy.
Two uses of wind energy
It is used to pump the ground water.
It is used to generate electricity with the
help of windmills.
Q31. How does weathercock (Wind vane) work?
It shows the direction in which the air is moving at that place. Thus,
if the wind is blowing from the north, the arrow will point towards the
Q32. Is it possible to light up a candle on the moon? Give
No, it is not possible to light up a candle on the moon because there is no
oxygen on the moon. Oxygen is one of the basic requirements for burning.
Q33. Earthworms come out of the soil during heavy rains. Why?
When it rains heavily, water fills up all the spaces occupied by the air in the
soil. In this situation, animals living in the soil such as earthworms have to
come out for respiration.
Q34. Why does the candle go off after some time when we cover it
with a glass tumbler?
The amount of oxygen component inside the glass is limited. When most of this oxygen
is used up by the burning candle, it can no longer burn and blows out.
Q35. What happens when air comes in contact with a cool surface?
When air comes in contact with a cool surface, air gets cooled and it can no
longer hold as much water vapor. Thus water vapor in the air condenses and drops
of water appear on cool surface.
Q36. Why long chimneys are preferred in factories?
The burning of fuel produces smoke. Smoke contains a few gases and fine dust particles
and is often harmful. Long chimneys in factories take the harmful smoke and
gases away from us.
Q37. What is the role of fine hair and mucus inside the nose?
We inhale air when we breathe through our nostrils. Fine hair and mucus are
present inside the nose to prevent dust particles from getting into the
Q38. Why do policemen regulating traffic at a crowded crossing
wear a mask to cover his face?
Policemen regulating traffic at a crowded crossing wear a mask to cover his
face to protect himself from the polluted air that emits from the vehicles
which may enters his nose and cause him serious problem.