c
(C) \(\,\frac{1}{\lambda }\,\, = \,\,{R_H}\,\left( {\frac{1}{{{n_1}^2}}\, - \,\frac{1}{{{n_2}^2}}} \right)\,\,\)

\(\therefore \,\,\frac{1}{\lambda }\,\, = \,\,1.907\, \times \,{10^{ - 7}}\,\left( {\frac{1}{{{1^2}}}\, - \,\frac{1}{{{\alpha ^2}}}} \right)\,\,\,\)

\(\therefore \,\,\lambda \,\, = \,\,\frac{1}{{1.097\, \times \,{{10}^7}}}\)\( = \,\,0.91\, \times \,{10^-7}\,\,\, = \,\,91\,\, \times \,{10^{ - 9}}\,\, = \,\,91\,\,nm\)