$\begin{array}{1 1}(a)\;23.6\times 10^{-31}Kg,3.9\times 10^{10}cm/s\\(b)\;35.6\times 10^{-31}Kg,2.9\times 10^{10}cm/s\\(c)\;21.6\times 10^{-31}Kg,1.9\times 10^{10}cm/s\\(d)\;23.6\times 10^{-19}Kg,2.9\times 10^{5}cm/s\end{array}$

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Mass of electron in Motion $=\large\frac{2}{931}$amu

$\Rightarrow \large\frac{2}{931}$$\times 1.66\times 10^{-27}kg$

$1amu=931MeV$

$\Rightarrow 35.6\times 10^{-31}kg$

Also $M_e=\large\frac{m_e^0}{\sqrt{1-\big(\Large\frac{v}{c}\big)^2}}$

$35.6\times 10^{-31}=\large\frac{\Large\frac{0.511}{931}\times 1.66\times 10^{-27}}{\sqrt{1-\big[\large\frac{u}{3\times 10^{10}}\big]^2}}$

$u=2.9\times 10^{10}cm/s$

Hence (b) is the correct answer.

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