MCQ practice · SSC Chemistry Board questions · Chapter 3: Structure of Matter
What is the angular momentum of the electron revolving in level C?
Think it through first, then pick an option.
- a 2.11 × 10⁻³⁴ m² kg/s
- b 3.16 × 10⁻³⁴ m²kg/s
- c 1.05 × 10⁻³⁴ m²kg/s
- d 1.58 × 10⁻³⁴ m² kg/s
Answer and explanation
Correct answer: b 3.16 × 10⁻³⁴ m²kg/s
C is the third level, n = 3; mvr = 3h/2π = 3 × 6.626 × 10⁻³⁴ ÷ 6.2832 ≈ 3.16 × 10⁻³⁴.
Why the other options are wrong
- a 2.11 × 10⁻³⁴ m² kg/s: This is the value for n = 2 (level B); C is the third level, n = 3: 3h/2π = 3.16 × 10⁻³⁴.
- c 1.05 × 10⁻³⁴ m²kg/s: This is n = 1 (level A), h/2π; C has n = 3.
- d 1.58 × 10⁻³⁴ m² kg/s: This fits no whole n; putting n = 3 gives 3.16 × 10⁻³⁴.
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