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In the first excited state of hydrogen atom, the energy of its electron is -3.4 eV. The radial distance of the electron from the hydrogen nucleus in this case is approximately: (Take 1 eV=1.6×10⁻¹⁹ J, e=1.6×10⁻¹⁹ C and 1/(4πε₀)=9×10⁹ N m² C⁻²)

Asked in NEET 2026 · Energy levels and ionisation

• (1) 2.1×10⁻¹¹ m
• (2) 2.1×10⁻¹⁰ m
• (3) 2.1×10⁻⁹ m
• (4) 2.1×10⁻⁸ m

Step-by-step solution

Why the other options are wrong

• (1) A power of ten low: 0.21 Å is smaller than the ground-state radius 0.53 Å, impossible for an excited state.
• (3) A power of ten high: 21 Å is far beyond the n=2 orbit (4×0.53=2.12 Å).
• (4) Two powers of ten high: 210 Å would be an orbit around n=20, not the first excited state.

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