1. Which of the following particles was discovered by J.J. Thomson?
A. Proton
B. Electron
C. Neutron
D. Positron
Answer: B. Electron
2. The charge and mass of an electron are:
A. -1.602 × 10⁻¹⁹ C and 9.109 × 10⁻³¹ kg
B. +1.602 × 10⁻¹⁹ C and 1.673 × 10⁻²⁷ kg
C. -1.602 × 10⁻¹⁹ C and 1.673 × 10⁻²⁷ kg
D. 0 and 1.008 amu
Answer: A. -1.602 × 10⁻¹⁹ C and 9.109 × 10⁻³¹ kg
3. Rutherford’s alpha particle experiment led to the discovery of:
A. Electron
B. Proton
C. Nucleus
D. Neutron
Answer: C. Nucleus
4. Which quantum number determines the shape of an orbital?
A. Principal quantum number (n)
B. Azimuthal quantum number (l)
C. Magnetic quantum number (m)
D. Spin quantum number (s)
Answer: B. Azimuthal quantum number (l)
5. The maximum number of electrons in a shell is given by:
A. 2n
B. n²
C. 2n²
D. n(n+1)
Answer: C. 2n²
6. Which of the following sets of quantum numbers is not allowed?
A. n = 2, l = 1, m = 0, s = +½
B. n = 3, l = 3, m = +1, s = -½
C. n = 4, l = 2, m = -1, s = +½
D. n = 1, l = 0, m = 0, s = -½
Answer: B. n = 3, l = 3, m = +1, s = -½
(l must be < n, so l = 3 is not valid when n = 3)
7. The number of orbitals in the d-subshell is:
A. 3
B. 5
C. 7
D. 10
Answer: B. 5
8. Which orbital will be filled after 3p according to the Aufbau principle?
A. 3d
B. 4s
C. 4p
D. 4f
Answer: B. 4s
9. The number of unpaired electrons in the ground state of oxygen (atomic number 8) is:
A. 0
B. 1
C. 2
D. 3
Answer: C. 2
10. Who proposed the concept of quantized energy levels for electrons in atoms?
A. J.J. Thomson
B. Rutherford
C. Bohr
D. Heisenberg
Answer: C. Bohr
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