Class 9 Science - Chapter Natural Resources NCERT Solutions | What are the two forms of oxygen found i

List any three human activities that you think would lead to air pollution.

What causes winds?

Why is the atmosphere essential for life?

Why do organisms need water?

Why is water essential for life?

We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?

List any three human activities which would lead to an increase in the carbon dioxide content of air.

How does the atmosphere act as a blanket?

How is our atmosphere different from the atmospheres on Venus and Mars?

You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?

Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?

State the universal law of gravitation.

Which of the following are matter?

Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.

A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?

What is meant by a pure substance?

How does the sound produced by a vibrating object in a medium reach your ear?

In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.

sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water

What are canal rays?

State any two conditions essential for good health.

Who discovered cells, and how?

Compare all the proposed models of an atom given in this chapter.

Give the names of the elements present in the following compounds.

(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.

What is the mass of:

(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?

What happens to the force between two objects, if
(i) the mass of one object is doubled?
(ii) the distance between the objects is doubled and tripled?
(iii) the masses of both objects are doubled?

The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ¹⁶₈ X and ¹⁸₈ X in the sample?

Which organelle is known as the powerhouse of the cell? Why?

Give reason for the following observations.

(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.

Write the electronic configuration of any one pair of isotopes and isobars.

If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide