Class 9 Science - Chapter Structure of the Atom NCERT Solutions | Compare all the proposed models of an at

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?

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

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

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.

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?

Describe Bohr’s model of the atom.

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.

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

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?

A sound wave travels at a speed of 339 m s^-1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?

Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?

Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in air and in aluminium to reach the second child.

How are simple tissues different from complex tissues in plants?

What are the two forms of oxygen found in the atmosphere?

Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

What is the physical state of water at—

(a) 25°C          (b) 0°C          (c) 100°C ?

What are the differences between animals belonging to the Aves group and those in the mammalia group?

Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.

What is meant by a pure substance?