d
The equilibrium stretching is given by equating weight with spring force.
$\therefore 0.2 \times 10=200 \times x$
$x=0.01 m=1 \mathrm{cm}$
When taken back to unstretched state, the sum of spring force and weight together is converted into spring force.
$\therefore 200 \times 0.01+0.2 \times 10=200 \times x$
$x=0.02 m=2 \mathrm{cm}$
The frequency is given by
$f=\frac{1}{2 \pi} \sqrt{\frac{k}{m}}=\frac{1}{2 \pi} \sqrt{\frac{200}{0.2}} \approx 5.05 H z$