The atom/ion is — Atomic Structure Chemistry Question

💡 Solution & Explanation

Wavelength 1654 Å corresponds to $E = \frac{12400}{1654} \approx 7.5$ eV. The transition from $n=2$ to $n=3$ gives $\Delta E = 13.6 Z^2 (\frac{1}{4} - \frac{1}{9}) = 13.6 Z^2 (\frac{5}{36}) = 1.888 Z^2$. Setting $1.888 Z^2 = 7.5 \implies Z^2 \approx 4 \implies Z=2$, which corresponds to He$^+$. Therefore, correct answer is C.