b
\(\begin{array}{l}
Let\,\theta \,be\,the\,angle\\
Which\,the\,particle\,makes\\
with\,an\,x - axis.\\
Form\,figure,\\
\,\,\,\,\,\,\,\,\,\,\,\tan \,\theta  = \frac{3}{{\sqrt 3 }} = \sqrt 3 \\
or,\,\,\,\,\,\,\theta \, = {\tan ^{ - 1}}\,\left( {\sqrt 3 } \right) = {60^ \circ }.
\end{array}\)