Class 9 Science - Chapter Structure of the Atom NCERT Solutions | Describe Bohr’s model of the atom.

If number of electrons in an atom is 8 and number of protons is also 8, then (i) what is the atomic number of the atom? and (ii) what is the charge on the atom?

For the symbol H,D and T tabulate three sub-atomic particles found in each of them.

With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.

Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and iv) Isobars. Give any two uses of isotopes.

Define valency by taking examples of silicon and oxygen.

Na⁺ has completely filled K and L shells. Explain.

Draw a sketch of Bohr’s model of an atom with three shells.

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

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

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 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

State any two conditions essential for good health.

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

Who discovered cells, and how?

Why should preventive measures and biological control methods be preferred for protecting crops?

Which of the following conditions will give the most benefits? Why?
(a) Farmers use high-quality seeds, do not adopt irrigation or use fertilizers.
(b) Farmers use ordinary seeds, adopt irrigation and use fertilizer.
(c) Farmers use quality seeds, adopt irrigation, use fertilizer and use crop protection measures.

Why is water essential for life?

An object has moved through a distance. Can it have zero displacement? If yes, support your answer with an example.

Convert into mole.

(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide.

What does the path of an object look like when it is in uniform motion?

A motorboat starting from rest on a lake accelerates in a straight line at a constant rate of 3.0 m s^-2 for 8.0 s. How far does the boat travel during this time?

What are the methods of preventing or reducing soil erosion?

An automobile vehicle has a mass of 1500 kg. What must be the force between the vehicle and road if the vehicle is to be stopped with a negative acceleration of 1.7 m s^-2?

What is immunisation?