d
Energy difference for infrared radiation will be smaller than those ultraviolet region.

Transition corresponding to Infra red region is:

\(2 \rightarrow 1 ; \frac{1}{\lambda}=R\left(1-\frac{1}{4}\right) \text { or } \lambda=\frac{4}{3 R}=12003 \mathrm{mm}(U V)\)

\(3 \rightarrow 2 ; \frac{1}{\lambda}=R\left(\frac{1}{4}-\frac{1}{9}\right) \quad o r \lambda=\frac{36}{5 R}\)

\(\lambda=\frac{36}{5} \times 91 n m=648 n m(\text {visible region})\)

\(4 \rightarrow 2 \frac{1}{\lambda}=R\left(\frac{1}{4}-\frac{1}{16}\right)=R \frac{3}{16}\)

\(\lambda=\frac{16}{3 R}=\frac{16}{3 R} \times 91 n m=480 n m(\text {visible})\)

\(4 \rightarrow 3 ; \frac{1}{\lambda}=R\left(\frac{1}{9}-\frac{1}{16}\right)=R\left(\frac{7}{144}\right)\)

\(\lambda=\frac{144}{7 R}=\frac{144}{7} \times 91 n m=1872 n m I R\)