a
\(\begin{array}{l}
Both\,Assertion\,and\,{\rm{Reason}}\,correct\,and\,{\rm{Reason}}\,is\,the\,correct\\
{\rm{explanation}}\,of\,Assertion.\\
Kinetic\,energy,\,E = \frac{1}{2}m{v^2}\\
Differenting\,both\,side\,\\
\frac{{\Delta E}}{E} = \frac{{\Delta m}}{m} + \frac{{2\Delta v}}{v}\\
\frac{{\Delta E}}{E} = \frac{1}{{100}} + 2 \times \frac{2}{{100}} = \frac{5}{{100}} = 5\% 
\end{array}\)