CBSE: Check NCERT based important questions (with answers) for CBSE 9th Science Exam 2020-21 on Chapter 4 (Structure Of The Atom). These are some of the most simple & conceptual questions of this chapter and can be solved in less than 5 minutes. Any student with sound knowledge of this chapter can attempt these questions. All the questions can also be asked in CBSE Class 9 Science exam 2020-21.
CBSE Class 9 Science Exam 2020-21: NCERT Based Important Extra Questions (With Answers) Chapter 4: Structure Of The Atom
Question: How many electrons are there in the L shell of a Chlorine atom?
Answer:
The electronic configuration of a Chlorine atom is 2, 8, 7. The L shell has eight electrons.
Question: Why does Argon have a zero valency?
Answer:
Argon has 8 electrons in their valence shells. As it has the maximum number of electrons in its valence shells and does not have any tendency to combine with other elements. So, its valency is equal to zero.
CBSE Class 9 Revised Syllabus for 2020-2021
Question: What were the drawbacks of Rutherford’s model of an atom?
Answer:
Rutherford concluded from the α-particle scattering experiment that–
- Most of the space inside the atom is empty because most of the α-particles
passed through the gold foil without getting deflected.
- Very few particles were deflected from their path, indicating that the positive
charge of the atom occupies very little space.
- A very small fraction of α-particles were deflected by 1800, indicating that all the positive charges and mass of the gold atom were concentrated in a very small volume within the atom. From the data, he also calculated that the radius of the nucleus is about
105 times less than the radius of the atom.
CBSE Class 9 Science Chapter Notes
Question: An element M has atomic number 2 and a mass number 4. Write the valency of this element?
Answer:
As K shell is completely filled, so the valency is zero.
Question: The electronic configuration of silicon is ____X___ and that of sulphur is ___Y___.
Choose the correct option.
(a) X = 2, 8, 6 & Y = 2, 8, 4
(b) X = 2, 8, 6 & Y = 2, 8, 4
(c) X = 2, 8, 6 & Y = 2, 8, 6
(d) X = 2, 8, 4 & Y = 2, 8, 4
Answer: (a)
Silicon — 2, 8, 4
Sulphur— 2, 8, 6
Question: What is the valency of Neon?
Answer:
The valency of Neon is 0.
Question: The mass number of an atom is equal to the number of nucleons in its nucleus.
(a) Proton
(b) Neutron
(c) Electron
(d) Nucleons
Answer:
(d) Nucleons.
The mass number of an atom is equal to the number of nucleons in its nucleus.
Question: In the alpha-particle scattering experiment, why did Ernest Rutherford use Gold foil instead of any other element?
Answer:
Gold is highly malleable and ductile. He selected a gold foil because he wanted as thin a layer as possible. This gold foil was about 1000 atoms thick.
Question: The mass of an electron is about _____ times the mass of an hydrogen atom.
(a)1/20000
(b) 1/200
(c) 1/2000
(d) 1/20
Answer: (c) 1/2000
The mass of an electron is about 1/2000 times the mass of an hydrogen atom. The mass of a proton and a neutron is taken as one unit each.
Question: What is the chemical formula of laughing gas?
Answer:
N2O.
The chemical formula of laughing gas is N2O, known as nitrous oxide (N2O) or dinitrogen monoxide.
