(a) The spring constant $k$ is proportional to the mass in the case of a simple pendulum. The numerator ($m$) and denominator ($d$) will cancel each other out. As a result, the simple pendulum’s time period is independent of the bob’s mass.
(b) The expression for the restoring force acting on the bob of a basic pendulum is
$F=-m g \sin \theta$
$F=$ restoring force
$\mathrm{m}=$ mass of the bob
$\mathrm{g}=$ acceleration due to gravity
$\theta=$ angle of displacement
When $\theta$ is small, $\sin \theta \approx \theta$.
Then the expression for the time period of a simple pendulum is given by $\mathrm{T}=2 \pi(\sqrt{I} / \sqrt{g})$
$sin \theta < \theta$ when $\theta$ is huge. As a result, the equation above is invalid. In the time period $T$, there will be an increase.