Relativistic correction become necessary when the expression for the kinetic energy $\large\frac{1}{2}$$mv^2$ becomes comparable with $mc^2$ where m is the mass of the particle . At what de- broglie wave length will relativistic correction become important for an electron ?

Question

$\begin{array}{1 1} \lambda = 10 nm \\ \lambda = 10^{-1}nm \\ \lambda= 10^{-4} nm \\ \lambda= 10^{-6} nm \end{array} $