Answer
a) the wavelength of the standing wave is less than $1.33\times 10^{-9}m$.
b) $\lambda_2=66.44\times 10^{-11}m$
Work Step by Step
(a) We know that $\lambda_n\propto n$. This relation shows that when $n$ increases then $\lambda_n$ increases as well. Thus, when the electron is in a state whose standing wave consisting of two wavelengths then the wavelength of the standing wave is less than $1.33\times 10^{-9}m$.
(b) As $n=2$, thus, $\lambda_2=2\pi(2)(5.29\times 10^{-11})$
$\lambda_2=66.44\times 10^{-11}m$
