A pendulum of length L swings from rest to rest n times in one second. The value of acceleration due to gravity is

• A

  $4{\mathrm{\pi }}^2{\mathrm{n}}^2\mathrm{L}$

• B

  $2{\mathrm{\pi }}^2{\mathrm{n}}^2\mathrm{L}$

• C

  ${\mathrm{\pi }}^2{\mathrm{n}}^2\mathrm{L}$

• D

  $\frac{{\mathrm{\pi }}^2{\mathrm{n}}^2\mathrm{L}}{2}$