The graph between the time period $(T)$ and the length $(l)$ of a simple pendulum is

Is the oscillation of a simple pendulum at the centre of the earth possible?

The motion of a simple pendulum executing $S.H.M.$ is represented by the following equation:
$Y = A \sin (\pi t + \phi)$,where time is measured in $seconds$.
The length of the pendulum is .............$cm$.

$A$ light balloon filled with helium of density $\rho_{He}$ is tied to a long light string of length $l$ and the string is attached to the ground. If the balloon is displaced slightly in the horizontal direction from the equilibrium and released,then:

$A$ pendulum clock that keeps correct time on the earth is taken to the moon. It will run (given that $g_{Moon} = g_{Earth}/6$):

Which of the following plots represents schematically the dependence of the time period of a pendulum,if measured and plotted as a function of the amplitude of its oscillations? (Note: amplitude need not be small)