d
According to the formula of Young's Modulus

\(E=\frac{F L}{A \Delta L}\)
where \(\Delta \mathrm{L}\) is the extension in the spring.
\(\mathrm{F}=\frac{\mathrm{EA} \Delta \mathrm{L}}{\mathrm{L}}\)            \(...(1)\)
Now, according to Hooke's law
\(\mathrm{F}=\mathrm{k} \Delta \mathrm{L}\)            \(...(2)\)
where \(\mathrm{k}\) is the spring constant By comparing \(( 1)\, and\, ( 2)\)
\(\mathrm{k} \Delta \mathrm{L}=\frac{\mathrm{EA} \Delta \mathrm{L}}{\mathrm{L}}\)
\(\quad \mathrm{k}=\frac{\mathrm{EA}}{\mathrm{L}}\)
Time period, \(\mathrm{T}=2 \pi \sqrt{\frac{\mathrm{M}}{\mathrm{k}}}\)
\(\mathrm{T}=2 \pi \sqrt{\frac{\mathrm{ML}}{\mathrm{EA}}}\)