Let nf,ni be the final and initial orbit. As we know that, λ1=109×107[nf21−ni21] Now, checking for each option, we get (a) λ1∝[321−421]=[91−161]=0.05… (i) (b) λ1∝[11−41]=0.75 ... (ii) (c) λ1∝[161−251]=0.0225 ... (iii) (d) λ1∝[41−91]=0.14 ... (iv) The option (b) has highest value. Since, frequency, f=λC⇒f∝λ1∴ Frequency will be maximum for transition n=2 to n=1.