In the Bohr model, the frequency of revolution of the electron in the n=2 orbit of He+ divided by that in the n=1 orbit of H is

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In the Bohr model, the frequency of revolution of the electron in the $n = 2$ orbit of $He X^{+}$ divided by that in the $n = 1$ orbit of $H$ is

Frequency

f = v /2 π r \propto (Z / n) / (n^{2} / Z) = Z^{2} / n^{3}

. For

He X^{+}

n = 2

4/8 = 1/2

. For H,

n = 1

1

. The ratio is

1/2