Class 9 Science - Chapter Structure of the Atom NCERT Solutions | If number of electrons in an atom is 8 a

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.

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?

A hockey ball of mass 200 g travelling at 10 m s^-1 is struck by a hockey stick so as to return it along its original path with a velocity at 5 m s^-1. Calculate the change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick.

Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?

Why is the plasma membrane called a selectively permeable membrane?

A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 metric tonnes (Hint: 1 metric tonne = 1000 kg.)

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

In the following example, try to identify the number of times the velocity of the ball changes: “A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team”.
Also identify the agent supplying the force in each case.

A racing car has a uniform acceleration of 4 m s^-2. What distance will it cover in 10 s after start?

What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?

How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25oC), which are miscible with each other?

Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?