Since the body is given just enough speed to complete the vertical circle

$u^2=5gR$

$v^2=u^2-2gR$

$\quad=5gR-2gR$

$\quad=3gR$

When the velocity is vertical, the body is acted by two acceleration $a_T='g'$ tangentially and centripetal acceleration $a_c=\large\frac{v^2}{R}$ radially.

$a_c=\large\frac{v^2}{R}=\frac{3gR}{R}$

$\quad=3g$

Total acceleration $=\sqrt {a_T^4+a_c^2}$

$\quad=\sqrt {g^2+3g^2}$

$\quad=g\sqrt {10}$

Hence a is the correct answer.

The V can also be found out using theorem of conservation of machanical energy.

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