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Practice each question, then open the answer or worked solution.
Which of the following statements is incorrect?
Ans: d) Air is present everywhere but not in soil.
Air is omnipresent and is present in soil too. This can be inferred by adding water to a pot filled with a lump of soil. After adding water it can be observed that the soil absorbs all the water and air bubbles are formed. These air bubbles show the escaping air.
Wind does not help in the movement of which of the following?
Ans: c) Ceiling fan
Wind does not help in the movement of ceiling fan because it moves by electricity.
What is not true about air?
Ans: d) it has no role in water cycle.
During the process of evaporation, the vapours of water are risen up by air to form clouds.
Mountaineers carry oxygen cylinders with them because
Ans: b) there is deficiency of oxygen on mountains at high altitude.
With increase in altitude, the atmosphere gets thinner and levels of oxygen decreases. This makes it difficult to breathe in higher altitudes as oxygen supply is reduced.
Boojho took an empty plastic bottle turned it upside down and dipped its open mouth into a bucket filled with water. He then tilted the bottle slightly and made the following observations.
i. Bubbles of air came out from the bottle.
ii. Some water entered the bottle.
iii. Nitrogen gas came out in the form of bubbles and oxygen got dissolved in water.
iv. No bubbles formed, only water entered the bottle.
Which observations is/are correct?
Ans: a) (i) and (ii)
When we dip an empty bottle in a bucket filled with water, the air trapped in the bottle starts escaping and tiny air bubbles are formed. Also, when he tilted the bottle, some water entered it because when the air escaped there was empty space left.
Which of the following components of air is present in the largest amount in the atmosphere?
Ans: a) Nitrogen
Atmospheric air contains all the four mentioned components but the component with the largest amount present in the air is nitrogen, which constitutes $78\% $ of the atmospheric air whereas oxygen constitutes $21\% $ and remaining $1\% $ is formed by water vapour, carbon dioxide, few other gases and dust particles.
The components of air which are harmful to living beings are
Ans: c) Dust and smoke
Dust and smoke are harmful to living beings because if they enter our body, they can cause respiratory problems.
Usha took a lump of dry soil in a glass and added water to it till it was completely immersed. She observed bubbles coming out. The bubbles contain
Ans: c) Air
When Usha poured water on the lump of soil, the air trapped in it got displaced and air bubbles were formed.