Chapter 7 - Quantam Theory of the Atom - Questions and Problems - Page 298: 7.118

Please see the work below.

We know that $\nu=\frac{E}{h}$ $\nu=\frac{7.1736\times 10^{-19}}{6.626\times 10^{-34}}=1.0826\times 10^{15}s^{-1}$ We also know that $\lambda=\frac{c}{\nu}$ We plug in the known values to obtain: $\lambda=\frac{2.998\times 10^8}{1.0826\times 10^{15}}=2.7691\times 10^{-7}m=276.91nm$