$\begin{array}{1 1}(a)\;6.6\times 10^{-10}&(b)\;3\times 10^{-10}\\(c)\;5\times 10^{-9}&(d)\;9.3\times 10^{-12}\end{array}$

Total energy=$\large\frac{-e^2}{2r_n}=$$-3.4eV=\large\frac{E_1}{n^2}$

$\therefore n^2=\large\frac{-13.6}{-3.4}$$=4$

$n=2$

Velocity=$\large\frac{u_1}{2}=\frac{2.18\times 10^8}{2}$$cm sec^{-1}$

$\therefore \lambda=\large\frac{h}{mu}$

$\Rightarrow \large\frac{6.6\times 10^{-27}\times 2}{9.108\times 10^{-28}\times 2.18\times 10^8}$

$\Rightarrow 6.6\times 10^{-10}$

Hence (a) is the correct answer.

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