alleryAn electron in a hydrogen atom falls from n = 4 to n = 2. The wavelength of the emitted photon (R_H = 1.097 × 10⁷ m⁻¹) is closest to:
A656 nm
B486 nm
C434 nm
D410 nm
Answer & Solution
Correct answer: B. 486 nm
1. 1/λ = R_H (1/n₁² − 1/n₂²) with n₁ = 2, n₂ = 4.
2. = 1.097 × 10⁷ × (1/4 − 1/16) = 1.097 × 10⁷ × 3/16 = 2.057 × 10⁶ m⁻¹.
3. λ = 1 / 2.057 × 10⁶ ≈ 4.86 × 10⁻⁷ m = 486 nm.
4. This is Hβ of the Balmer series — blue-green line.
_Source: syllabus Chem Ch 2 §2.3 Hydrogen Spectrum (Balmer)_
Keep practising Chemical Thermodynamics
Browse all Chemical Thermodynamics questions for AP Intermediate 1st Year, or explore more Chemistry topics.
Related questions
A process whose enthalpy and entropy changes share the same arithmetic sign will show:At minus 10.00 degrees Celsius the entropy change of the universe for melting is negative,Melting is described as spontaneous at 10.00 degrees Celsius because at that temperature:K_sp of a sparingly soluble salt AB at 25 °C is 4 × 10⁻¹⁰. Molar solubility s of AB is:A buffer solution is most resistant to pH change when:K_w (ionic product of water at 25 °C) is:The pH of a 0.01 M HCl solution is:For an exothermic reaction at equilibrium, raising the temperature: