Heat treatment of muscular pain involves radiation of wavelength of about 900 nm . Which spectral line of Hatom is suitable for this purpose?
$$
\left[\mathrm{R}_{\mathrm{H}}=1 \times 10^5 \mathrm{~cm}, \mathrm{~h}=6.6 \times 10^{-34} \mathrm{JS}, \mathrm{c}=3 \times 10^8 \mathrm{~ms}^{-1}\right]
$$