An electron of hydrogen atom on an excited state is having energy E...

Energy of ${n}^{th}$ orbit is given by, ${E}_{n} = - \dfrac{13 . 6}{{n}^{2}}$

$⇒ - \dfrac{13 . 6}{{n}^{2}} = - 0 . 85 ⇒ n = 4$

No of transition,

$= \dfrac{n ( n - 1 )}{2} = \dfrac{4 ( 4 - 1 )}{2} = 6$