In the Bohr model, which pair of hydrogen-like species and levels has the same total electron energy?

A $Li X^{2 +}$ , $n = 2$ and $He X^{+}$ , $n = 2$
B $He X^{+}$ , $n = 1$ and $H$ , $n = 2$
C $He X^{+}$ , $n = 2$ and $H$ , $n = 1$
D $Be X^{3 +}$ , $n = 2$ and $H$ , $n = 1$

Answer: C

E = -13.6

Z^{2} / n^{2}

eV. He+ (n=2): -13.6; H (n=1): -13.6. These match. The others give Li2+ (n=2) -30.60, He+ (n=1) -54.4, H (n=2) -3.4, Be3+ (n=2) -54.4 eV, none equal in their pair.

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