Answer:
4. [tex]f=\frac{1}{2\pi}\sqrt{\frac{g}{L}}[/tex]
Explanation:
We have in this case a simple pendulum, of length L and mass m. As we know, the period of this pendulum is:
[tex]T\sim 2\pi \sqrt{\frac{L}{g}}[/tex]
but it is true only in small oscillation angles, it meas less than 1 rad.
The frequency is the inverse of the period, then:
[tex]f=\frac{1}{T}=\frac{1}{2\pi}\sqrt{\frac{g}{L}}[/tex]
The correct answer is 4.
I hope it helps you!