Ncert – class 9- science – Chapter 4 – Structure of the Atom 2 Welcome to your Ncert - class 9- science - Chapter 4 – Structure of the Atom 2 1. The expression for Bohr's radius of an atom is $$r=\frac{n^{2}h^{2}}{4\pi^{2}m^{2}e^{2}z^{2}}$$ $$r=\frac{n^{2}h^{2}}{4\pi^{2}me^{2}z}$$ $$r=\frac{n^{2}h^{2}}{4\pi^{2}me^{2}z^{2}}$$ $$r=\frac{n^{2}h^{2}}{4\pi^{2}me^{4}z^{2}}$$ None 2. Which of the following is not a correct statement according to Rutherford's atomic model? Electrons revolve around the nucleus in a fixed circular path. The size of nucleus is very small in comparison to the atom. Most of the part inside the atom is empty. 99% of mass of an atom is centered in the nucleus. None 3. Which of the following statements about Rutherford’s model of atom are correct?(i) Proposed that nearly all the mass of an atom resides in the nucleus.(ii) Established that the �α–particles are four times as heavy as a hydrogen atom.(iii) Considered the nucleus as positively charged.(iv) Agreed with Thomson’s model. (i) and (iv) (i) and (iii) only (i) (ii) and (iii) None 4. The presence of electrons outside the nucleus and nucleus at the centre of the atom was suggested by: Electrons by J.J. Thomson and nucleus by E. Goldstein Electrons by J.J. Thomson and nucleus by E. Rutherford Electrons by J. Chadwick and nucleus by E. Rutherford Electrons by E. Rutherford and nucleus by J.J. Thomson None 5. The ratio of the radii of the first three Bohr orbits is: 1:8:27 1:2:3 1:5:33 1:4:9 None 6. The sum of number of protons and number of neutrons present in the nucleus of an atom is called its atomic number all of the above mass number number of electrons None 7. Neutron is a fundamental particle carrying: A charge of −1 and a mass of 1 unit No charge and a mass of 1 unit No charge and no mass A charge of +1 unit and a mass of unit None 8. If an electron moves away from nucleus, its potential energy: not changes increases none of these decreases None 9. Which one of the following is considered as the main postulate of Bohr's model of atom Electrons are revolving around the nucleus Centrifugal force produced due to the revolving electrons balances the force of attraction between electron and protons Angular momentum of electron is an integral multiple of h/2π Protons are present in the nucleus None 10. The introduction of a neutron into the nuclear composition of an atom would lead to a change in: Its atomic weight The chemical nature of the atom The number of the electrons also Its atomic number None 11. Bohr's theory can be applied to determine the? first ionization energy of Be atom second ionization energy of helium atom Electronegativity of Li 2+ ion electron gain enthalpy of hydrogen atom None 12. The radius of the first Bohr orbit of hydrogen atom is r. The radius of the 3 rd orbit would be: 27r 3r 9r None of these None 13. Goldsteins experiments which involved passing high voltage electricity through gases at very low pressure resulted in the discovery of: Electron Nucleus Neutron Proton None 14. The nucleus of helium contains Four neutrons Two neutrons and two protons Four protons Four protons and two electrons None 15. How many sub-atomic particles are present in an α- particle used in Rutherford's scattering experiment? Protons - 2, Neutrons - 0, Electron - 2 Protons - 2, Neutron - 2, Electron - 1 Protons - 4, Neutrons - 0, Electrons - 0 Protons - 2, Neutron - 2, Electron - 0 None Time's up Please Share This Share this content Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Opens in a new window Leave a Reply Cancel replyCommentEnter your name or username to commentEnter your email address to commentEnter your website URL (optional) Save my name, email, and website in this browser for the next time I comment.
