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Question:

The radius of the second Bohr orbit for the hydrogen atom is: [Given: Planck's const. h=6.6262×10⁻³⁴Js; mass of electron=9.1091×10⁻³¹kg; charge of electron, e=1.60210×10⁻¹⁹C; permittivity of vacuum, ε₀=8.854185×10⁻¹²kg⁻¹m⁻³A²]

4.76 ˚A

0.529 ˚A

2.12 ˚A

1.65 ˚A

Solution:

r=n²h²/4π²me²k
r=2²(6.6262×10⁻³⁴Js)²/4×(3.1416)²×9.1091×10⁻³¹kg×(1.60210×10⁻¹⁹C)²×9×10⁹
r=2.12×10⁻¹⁰m
r=2.12 ˚A
Hence, the option (C) is the correct answer.