Number of bright lines in the emissions spectrum will be

Question

In a sample of hydrogen  like atoms  all of which are in ground state , a photon beam containing  photons of various  energies  is passed.  In absorption  spectrum , five dark lines are observed.  The number of bright lines in the emissions  spectrum  will be

A) 5

B)10

C) 15

D) none

Answer 1

Sigma of n-1 n= 6 

since 5 dark lines 

so Sigma of r-1 

where r goes to 6 

=>15