Class 9 Science - Chapter Structure of the Atom NCERT Solutions | What do you think would be the observati

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.

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

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

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

Describe Bohr’s model of the atom.

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?

A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?

Explain how defects in a metal block can be detected using ultrasound.

You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?

List the points of differences between homogeneous and heterogeneous mixtures.

Give reasons for the following observation:

The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.

Under which of the following conditions are you most likely to fall sick?
(a) when you are taking examinations.
(b) when you have travelled by bus and train for two days.
(c) when your friend is suffering from measles.

Why?

What is the physical state of water at—

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

Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of their cell wall.

Which of the following is true for displacement?

(a) It cannot be zero.
(b) Its magnitude is greater than the distance travelled by the object.