When gaseous hydrogen at room temperature is bombarded with \(12.75\,\text{eV}\) electrons, the maximum possible number of spectral lines emitted is
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If an atom is excited up to the level \(n\), the maximum possible number of emission lines is
\[
\boxed{
N=\frac{n(n-1)}{2}.
}
\]
For hydrogen,
\[
E_n=13.6\left(1-\frac1{n^2}\right)\text{ eV}.
\]