As the temperature rises, the time period of a pendulum

The time period of a simple pendulum is given by $T = 2\pi \sqrt{\dfrac{l}{g}}$

As the temperature increases, the length $l$ of the pendulum increases due to linear thermal expansion, given by $l' = l(1 + \alpha \Delta \theta)$

Since $T \propto \sqrt{l}$, an increase in the length of the pendulum leads to an increase in its time period.

Thus, the time period of the pendulum increases.