Structure of atom very important questions

Read Time:6 Minute, 27 Second

1. Who discovered the electron?
A) J.J. Thomson
B) Rutherford
C) Niels Bohr
D) James Chadwick
✅ Answer: A) J.J. Thomson

2. Which experiment led to the discovery of the nucleus in an atom?
A) Cathode ray experiment
B) Gold foil experiment
C) Oil drop experiment
D) Hydrogen spectrum analysis
✅ Answer: B) Gold foil experiment

3. Cathode rays are composed of:
A) Protons
B) Neutrons
C) Electrons
D) Alpha particles
✅ Answer: C) Electrons

4. Who proposed the “Plum Pudding Model” of the atom?
A) Rutherford
B) Bohr
C) J.J. Thomson
D) Dalton
✅ Answer: C) J.J. Thomson

5. What is the charge of a proton?
A) -1
B) 0
C) +1
D) +2
✅ Answer: C) +1

6. Which of the following is neutral?
A) Electron
B) Proton
C) Neutron
D) Positron
✅ Answer: C) Neutron

7. Who discovered the neutron?
A) J.J. Thomson
B) James Chadwick
C) Niels Bohr
D) Rutherford
✅ Answer: B) James Chadwick

8. In Rutherford’s model, electrons revolve around the nucleus in:
A) Zigzag paths
B) Random orbits
C) Fixed circular orbits
D) Elliptical orbits
✅ Answer: C) Fixed circular orbits

9. According to Bohr’s model, electrons revolve in:
A) Spiral paths
B) Continuous orbits
C) Discrete energy levels
D) Random orbits
✅ Answer: C) Discrete energy levels

10. What does the atomic number represent?
A) Number of electrons + neutrons
B) Number of neutrons
C) Number of protons
D) Mass of the atom
✅ Answer: C) Number of protons

11. Which of the following is a pair of isotopes?
A) Sodium and Potassium
B) Hydrogen and Deuterium
C) Carbon and Oxygen
D) Calcium and Argon
✅ Answer: B) Hydrogen and Deuterium

12. Isobars have:
A) Same atomic number, different mass number
B) Same mass number, different atomic number
C) Same number of electrons
D) Same number of protons
✅ Answer: B) Same mass number, different atomic number

13. What is the total number of electrons in a neutral atom of carbon (atomic number 6)?
A) 3
B) 6
C) 12
D) 18
✅ Answer: B) 6

14. The maximum number of electrons that can be accommodated in the second shell (L shell) is:
A) 2
B) 4
C) 8
D) 18
✅ Answer: C) 8

15. Which of the following elements has the same number of protons and electrons in a neutral atom?
A) Ion
B) Atom
C) Isotope
D) Molecule
✅ Answer: B) Atom

16. Which subatomic particle was discovered last?
A) Electron
B) Proton
C) Neutron
D) Positron
✅ Answer: C) Neutron

17. Which particle is responsible for the identity of an element?
A) Electron
B) Proton
C) Neutron
D) Nucleus
✅ Answer: B) Proton

18. The mass number of an atom is the sum of:
A) Protons and electrons
B) Protons and neutrons
C) Neutrons and electrons
D) Electrons only
✅ Answer: B) Protons and neutrons

19. What is the maximum number of electrons in the third shell (M shell)?
A) 2
B) 8
C) 18
D) 32
✅ Answer: C) 18

20. Which of the following is not true about isotopes?
A) They have the same atomic number
B) They have different numbers of neutrons
C) They have different chemical properties
D) Their mass numbers are different
✅ Answer: C) They have different chemical properties

21. What is the electron configuration of sodium (atomic number 11)?
A) 2, 8
B) 2, 8, 1
C) 2, 1, 8
D) 1, 8, 2
✅ Answer: B) 2, 8, 1

22. Which scientist explained that electrons are arranged in shells around the nucleus?
A) J.J. Thomson
B) Bohr
C) Rutherford
D) Dalton
✅ Answer: B) Bohr

23. Which of the following pairs are isobars?
A) $_{19}^{39}K$ and $_{20}^{40}Ca$
B) $_{6}^{14}C$ and $_{7}^{14}N$
C) $_{1}^{1}H$ and $_{1}^{2}H$
D) $_{17}^{35}Cl$ and $_{17}^{37}Cl$
✅ Answer: B) $_{6}^{14}C$ and $_{7}^{14}N$

24. The nucleus of an atom contains:
A) Only electrons
B) Protons and neutrons
C) Only protons
D) Only neutrons
✅ Answer: B) Protons and neutrons

25. Which of the following particles has the least mass?
A) Proton
B) Neutron
C) Electron
D) Alpha particle
✅ Answer: C) Electron

26. The deflection of alpha particles in Rutherford’s experiment showed that:
A) Atoms have no charge
B) Atoms are mostly empty space
C) Electrons are heavy
D) Nucleus is negatively charged
✅ Answer: B) Atoms are mostly empty space

27. Which element is used in Bohr’s atomic model for explanation?
A) Helium
B) Hydrogen
C) Oxygen
D) Lithium
✅ Answer: B) Hydrogen

28. What is the charge on an alpha particle?
A) +1
B) +2
C) -1
D) 0
✅ Answer: B) +2

29. How many neutrons are present in $_{11}^{23}Na$ ?
A) 11
B) 23
C) 12
D) 34
✅ Answer: C) 12

30. Which one of the following is NOT a part of Dalton’s atomic theory?
A) All matter is made of indivisible atoms
B) Atoms of the same element are identical
C) Atoms combine in whole-number ratios
D) Atoms contain a nucleus
✅ Answer: D) Atoms contain a nucleus

Assertion and Reason type questions

Each question has two statements:

Assertion (A)
Reason (R)

You must choose the correct option:

Options:
A) Both A and R are true, and R is the correct explanation of A
B) Both A and R are true, but R is not the correct explanation of A
C) A is true, but R is false
D) A is false, but R is true.

1.
Assertion (A): Electrons revolve around the nucleus in fixed orbits.
Reason (R): Rutherford explained that electrons are present in circular orbits around the nucleus.
✅ Answer: C) A is true, but R is false

2.
Assertion (A): Neutrons are found in the nucleus of all atoms except hydrogen.
Reason (R): Hydrogen has only one proton and no neutron.
✅ Answer: A) Both A and R are true, and R is the correct explanation of A

3.
Assertion (A): The mass number of an atom is always greater than the atomic number.
Reason (R): Mass number is the sum of protons and neutrons.
✅ Answer: A) Both A and R are true, and R is the correct explanation of A

4.
Assertion (A): Cathode rays are positively charged.
Reason (R): Cathode rays are made up of protons.
✅ Answer: D) A is false, but R is true
(Cathode rays are negatively charged and consist of electrons.)

5.
Assertion (A): Isotopes have different chemical properties.
Reason (R): Isotopes have different numbers of neutrons.
✅ Answer: C) A is false, but R is true
(Isotopes have similar chemical properties because they have the same number of electrons.)

6.
Assertion (A): Bohr’s model of the atom explained the stability of atoms.
Reason (R): Electrons in Bohr’s model do not lose energy while revolving in fixed orbits.
✅ Answer: A) Both A and R are true, and R is the correct explanation of A

7.
Assertion (A): In a neutral atom, the number of protons is equal to the number of electrons.
Reason (R): Protons and electrons have equal and opposite charges.
✅ Answer: A) Both A and R are true, and R is the correct explanation of A

8.
Assertion (A): Electrons are present inside the nucleus.
Reason (R): The nucleus contains most of the atom’s mass.
✅ Answer: D) A is false, but R is true

9.
Assertion (A): Rutherford’s alpha particle experiment showed that the nucleus is very small compared to the atom.
Reason (R): Most alpha particles passed through the gold foil without any deflection.
✅ Answer: A) Both A and R are true, and R is the correct explanation of A

10.
Assertion (A): Isobars have different mass numbers but the same atomic number.
Reason (R): Isobars have different numbers of neutrons.
✅ Answer: D) A is false, but R is true
(Isobars have the same mass number but different atomic numbers.)

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