Chapter 7 - Sections 7.1-7.6 - Exercises - Problems by Topic - Page 331: 70a

$1.60\times10^{14}\,Hz$

$\Delta E_{atom}= -2.18\times10^{-18}\,J(\frac{1}{n_{f}^{2}}-\frac{1}{n_{i}^{2}})$ $= -2.18\times10^{-18}\,J(\frac{1}{3^{2}}-\frac{1}{4^{2}})$ $=-1.05972\times10^{-19}\,J$ $E_{photon}=-\Delta E_{atom}=1.05972\times10^{-19}\,J$ $E=h\nu\implies \nu=\frac{E}{h}$ $=\frac{1.05972\times10^{-19}\,J}{6.626\times10^{-34}\,J\cdot s}$ $=1.60\times10^{14}\,Hz$