Answer
$0.0$ Hz
Work Step by Step
The formula for the period is:
$$T=2\pi \sqrt{\frac{l}{g}}$$
We also that frequency is:
$$f=\frac{1}{T}$$
Combining the two formulas;
$$f=\frac{1}{2\pi} \sqrt{\frac{g}{l}}$$
Since the pendulum is in free fall, the apparent gravity is actually $9.8m/s^2-9.8m/s^2=0m/s^2$, or "zero gravity". Therefore, the frequency is:
$$f=\frac{1}{2\pi} \sqrt{\frac{0.0m/s^2}{2.0m}}=0.0 Hz$$
