NCERT Solutions For Class 9 Science

What are canal rays?

If an atom contains one electron and one proton, will it carry any charge or not?

On the basis of Thomson's model of an atom, explain how the atom is neutral as a whole.

On the basis of Rutherford's model of an atom, which sub-atomic particle is present in the nucleus of an atom?

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

4. What do you think would be the observation if the \alpha-particle scattering experiment is carried out using a foil of a metal other than gold?

Name the three sub-atomic particles of an atom.

Write the distribution of electrons in carbon and sodium atoms.

If K and L shells of an atom are full, then what would be the total number of electrons in 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?

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.

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

Compare the properties of electrons, protons and neutrons.

What are the limitations of J.J. Thomson’s model of the atom?

What are the limitations of Rutherford’s model of the atom?

Describe Bohr’s model of the atom.

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

Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.

Define valency by taking examples of silicon and oxygen.

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

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

If bromine atom is available in the form of, say, two isotopes ^{79}_{35}\text{Br} (49.7%) and ^{81}_{35}\text{Br} (50.3%), calculate the average atomic mass of bromine atom.

The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ^{16}_{8}\text{X} and ^{18}_{8}\text{X} in the sample?

If Z = 3, what would be the valency of the element? Also, name the element.

Composition of the nuclei of two atomic species X and Y are given as under

\quad\quad\quad\quad\quad\quad\quadX\quadY
Protons \quad=\,\, 6 \quad 6
Neutrons \,=\,\, 6 \quad 8
Give the mass numbers of X and Y. What is the relation between the two species?

For the following statements, write T for True and F for False.
(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
(c) The mass of an electron is about \frac{1}{2000} times that of proton.
(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.

Put tick (\checkmark) against correct choice and cross (\times) against wrong choice in questions 15, 16 and 17

Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
(a) Atomic Nucleus  (b) Electron
(c) Proton  (d) Neutron

Isotopes of an element have
(a) the same physical properties
(b) different chemical properties
(c) different number of neutrons
(d) different atomic numbers.

Number of valence electrons in Cl ^- ion are:
(a) 16 \quad\quad (b) 8 \quad\quad (c) 17 \quad\quad (d) 18

Which one of the following is a correct electronic configuration of sodium?
(a) 2,8 \quad\quad (b) 8,2,1 \quad (c) 2,1,8 \quad\quad (d) 2,8,1.

Complete the following table.