The general formula for calculating number of spectral lines is$= \frac{ ({\mathrm{n}}_{2 }-{\mathrm{n}}_1)({\mathrm{n}}_2 -{\mathrm{n}}_1+1) }{2}$

Given,n₂=6, n₁=2

Number of spectral lines$$\begin{gathered} = \frac{ (6-2)(6 -2+1) }{2} \\ =10 \end{gathered}$$

These spectral lines belongs to balmer series of the hydrogen spectrum

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