Atomic Structure | First Year Chemistry Past Paper MCQs | mosaicbro.com

Atomic Structure | First Year Chemistry Past Paper MCQs

7 of 44 questions (Page 4 of 7)

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22 When 4s orbital is complete, the electron goes into:
Correct Answer: B
Explanation: After 4s fills, electrons occupy 3d (Aufbau principle: 3d has lower n+l than 4p).
23 The limiting line of Balmer series lies in the region:
Correct Answer: A
Explanation: Balmer's limiting line (n=∞→2) is at 364.6 nm (visible/UV boundary).
24 Which of the following orbitals is dumb bell shaped?
Correct Answer: B
Explanation: p-orbitals (l=1) have a dumbbell shape with two lobes.
25 Free neutron decays into a proton with the emission of an electron and a ___.
Correct Answer: B
Explanation: Free neutron decay: n → p + e⁻ + ν̄ₑ (antineutrino).
26 The mass of an oxygen atom is:
Correct Answer: A
Explanation: Mass of 1 O atom ≈ 16 u = 16 × 1.661 × 10⁻²⁴ g = 2.657 × 10⁻²³ g.
27 The electrons occupying an orbital are distinguished by:
Correct Answer: D
Explanation: Pauli exclusion principle: electrons in same orbital have opposite spins (mₛ = ±½).
28 The mass of proton is (in kg):
Correct Answer: C
Explanation: Proton mass = 1.6726 × 10⁻²⁷ kg.
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