As we know that time period of simple pendulum will be
[tex]T = 2\pi \sqrt{\frac{L}{g}}[/tex]
now we will have
time period of a clock on the surface of earth will be 1 s where we have acceleration due to gravity is g = 9.8 m/s/s
now if we took the pendulum to the surface of moon where acceleration due to gravity will be 1.65 m/s/s then this time period will change
so we will say by above equation
[tex]\frac{T_{earth}}{T_{moon}} =\sqrt{ \frac{g_{moon}}{g_{earth}}}[/tex]
now we will have
[tex]T_{moon} = \sqrt{\frac{g_{earth}}{g_{moon}}}T_{earth}[/tex]
now plug in all data in this
[tex]T_{moon} = \sqrt{\frac{9.8}{1.65}}(1s)[/tex]
[tex]T_{moon} = 2.44 s[/tex]
so time period on moon will be 2.44 s