(a) Here, Mass of the body, $m = 500g = 500 \times 10^{- 3}kg$
Spring constant, $k = 8\pi^{2}\ N\ m^{- 1}$
The frequency of oscillation is
$v = \frac{1}{2\pi}\sqrt{\frac{k}{m}} = \frac{1}{2\pi}\sqrt{\frac{8\pi^{2}\ {N\ m}^{- 1}}{500 \times 10^{- 3}\ kg}} = 2\ Hz$