For maximum radius the escape speed should just match the speed of light. For smaller radius than this maximum radius, the escape speed would be even higher prohibiting escape of anything.

So, $v_e = c= \sqrt \frac {2GM}{R_{max}}$

$\therefore R_{max} = \frac {2GM}{c^2} = \frac {2\times 6.67 \times 10^{-11} \times 6.0 \times 10^{24} }{(3\times 10^8 )^2}$

$\therefore R_{max} = 8.9$ mm

Hence, (D)