Answer :
The period of a pendulum is related to its frequency by the following formula:
[tex]T=\frac{1}{f}[/tex]If the frequency is halved we have:
[tex]T_2=\frac{1}{\frac{f}{2}}[/tex]Simplifying we get:
[tex]T_2=2(\frac{1}{f})[/tex]The term inside the parenthesis is the original period, therefore:
[tex]T_2=2T[/tex]Therefore, if the frequency is halved the period is doubled.