The wave number of the last line of the Balmer series in hydrogen spectrum is given by
\(\frac{1}{\lambda } = R\left( {\frac{1}{{{2^2}}} - \frac{1}{{{\infty ^2}}}} \right) = \) \(\frac{R}{4} = \frac{{{{10}^7}}}{4} = 0.25 \times {10^7}{{\text{m}}^{ - 1}}\)