ETEA / KMU MDCAT (KPK) Chemistry Atomic Structure — Set 2

ETEA / KMU MDCAT (KPK) Chemistry Atomic Structure — Set 2

1. Question 1

   Q1. The energy of an electron in a hydrogen atom is determined by which quantum number?

   • A) Azimuthal
   • B) Magnetic
   • C) Principal
   • D) Spin

   Answer: Principal

   Explanation: Principal quantum number determines energy level in hydrogen atom; azimuthal quantum number affects energy in multi-electron atoms.

2. Question 2

   Q2. What is the maximum number of electrons that can occupy an orbital with n=3 and l=2?

   • A) 2
   • B) 5
   • C) 10
   • D) 18

   Answer: 10

   Explanation: l=2 indicates a d-orbital, which can hold 10 electrons; n=3 doesn't change this capacity.

3. Question 3

   Q3. The atomic number of an element is equal to the number of

   • A) Protons + Neutrons
   • B) Protons
   • C) Electrons + Neutrons
   • D) Neutrons

   Answer: Protons

   Explanation: Atomic number equals proton count; neutron count varies among isotopes of the same element.

4. Question 4

   Q4. The wavelength of a spectral line in the hydrogen spectrum can be calculated using which equation?

   • A) de Broglie
   • B) Heisenberg's Uncertainty Principle
   • C) Rydberg
   • D) Schrödinger

   Answer: Rydberg

   Explanation: Rydberg equation predicts spectral lines in hydrogen; de Broglie relates to particle wavelength, not spectral lines.

5. Question 5

   Q5. For a given principal quantum number n, the possible values of azimuthal quantum number l are

   • A) 0 to n
   • B) 1 to n
   • C) 0 to n-1
   • D) 1 to n-1

   Answer: 0 to n-1

   Explanation: l ranges from 0 to n-1; for n=3, l can be 0, 1, or 2.

6. Question 6

   Q6. The energy required to remove an electron from a neutral atom is called

   • A) Electronegativity
   • B) Ionization Energy
   • C) Electron Affinity
   • D) Atomic Radius

   Answer: Ionization Energy

   Explanation: Ionization energy is the energy to remove an electron; electronegativity is the tendency to attract electrons.

7. Question 7

   Q7. The orbital with the highest energy in a multi-electron atom has the quantum numbers n=4, l=1. What type of orbital is this?

   • A) s
   • B) p
   • C) d
   • D) f

   Answer: p

   Explanation: l=1 corresponds to a p-orbital; n=4 indicates it's a 4p orbital.

8. Question 8

   Q8. The number of unpaired electrons in a nitrogen atom (Z=7) is

   • A) 1
   • B) 2
   • C) 3
   • D) 4

   Answer: 3

   Explanation: Nitrogen's electron configuration is 1s² 2s² 2p³, with 3 unpaired electrons in 2p orbitals.

9. Question 9

   Q9. The Pauli Exclusion Principle states that

   • A) Two electrons in the same atom can have the same set of quantum numbers
   • B) Two electrons in the same orbital must have opposite spins
   • C) Electrons occupy the lowest available energy levels
   • D) Orbitals are filled in order of increasing energy

   Answer: Two electrons in the same orbital must have opposite spins

   Explanation: Pauli Exclusion Principle states that no two electrons can have the same set of quantum numbers, implying opposite spins in the same orbital.

10. Question 10

    Q10. The element with the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ is

    • A) Potassium
    • B) Calcium
    • C) Scandium
    • D) Argon

    Answer: Potassium

    Explanation: The given configuration corresponds to potassium (Z=19); calcium has an additional electron in 4s.

11. Question 11

    Q11. The frequency of a spectral line is related to the energy difference between two levels by

    • A) ΔE = hν
    • B) λ = h/p
    • C) E = mc²
    • D) ν = c/λ

    Answer: ΔE = hν

    Explanation: ΔE = hν relates energy difference to frequency; λ = h/p is de Broglie's equation for particle wavelength.

12. Question 12

    Q12. The azimuthal quantum number l=3 corresponds to which type of orbital?

    • A) s
    • B) p
    • C) d
    • D) f

    Answer: f

    Explanation: l=3 corresponds to f-orbitals; l=0, 1, and 2 correspond to s, p, and d orbitals, respectively.

13. Question 13

    Q13. The effective nuclear charge experienced by an outer electron in a multi-electron atom is

    • A) Less than the actual nuclear charge
    • B) Equal to the actual nuclear charge
    • C) More than the actual nuclear charge
    • D) Zero

    Answer: Less than the actual nuclear charge

    Explanation: Inner electrons shield outer electrons, reducing the effective nuclear charge they experience.

14. Question 14

    Q14. The radius of an atomic nucleus is approximately

    • A) 10⁻¹⁰ m
    • B) 10⁻¹⁵ m
    • C) 10⁻¹⁸ m
    • D) 10⁻¹² m

    Answer: 10⁻¹⁵ m

    Explanation: Nuclear radius is about 10⁻¹⁵ m; atomic radius is about 10⁻¹⁰ m.

15. Question 15

    Q15. The Heisenberg Uncertainty Principle is mathematically expressed as

    • A) Δx * Δp >= h/4π
    • B) ΔE * Δt >= h/4π
    • C) λ = h/p
    • D) Both A and B

    Answer: Both A and B

    Explanation: Heisenberg's principle is expressed as Δx * Δp >= h/4π and ΔE * Δt >= h/4π; λ = h/p is de Broglie's equation.

16. Question 16

    Q16. The maximum number of electrons that can occupy the M-shell (n=3) is

    • A) 8
    • B) 18
    • C) 32
    • D) 50

    Answer: 18

    Explanation: For n=3, l can be 0, 1, or 2, corresponding to s, p, and d orbitals, which can hold 2+6+10=18 electrons.

17. Question 17

    Q17. The quantum number that describes the orientation of an orbital in space is

    • A) Principal
    • B) Azimuthal
    • C) Magnetic
    • D) Spin

    Answer: Magnetic

    Explanation: Magnetic quantum number (m_l) determines the orientation of an orbital; spin quantum number determines electron spin.

18. Question 18

    Q18. The energy of an electron in an atom is quantized, meaning it can only take on certain discrete values. This is a consequence of

    • A) Heisenberg Uncertainty Principle
    • B) de Broglie's hypothesis
    • C) Schrödinger equation
    • D) Pauli Exclusion Principle

    Answer: Schrödinger equation

    Explanation: Schrödinger equation leads to quantized energy levels; Heisenberg's principle relates to measurement uncertainty.

19. Question 19

    Q19. The number of electrons in a neutral atom of chromium (Z=24) that have l=2 is

    • A) 4
    • B) 5
    • C) 6
    • D) 8

    Answer: 5

    Explanation: Chromium's electron configuration is [Ar] 3d⁵ 4s¹; 5 electrons are in 3d orbitals (l=2).

20. Question 20

    Q20. The spin quantum number of an electron can have values

    • A) +1/2 or -1/2
    • B) +1 or -1
    • C) 0 or 1
    • D) +2 or -2

    Answer: +1/2 or -1/2

    Explanation: Spin quantum number can be +1/2 or -1/2; other options are not valid for electron spin.