Answer: Solubility
Solubility is the ability to be dissolved. Saturation is when the concentration is too high(more than solubility) that when you add another material it won't dissolve. Solute is the material that dissolved. Solvent is the material that used for dissolving
Explanation:
Let f is the frequency of an oscillation and T is the period of the oscillation. There exists an inverse relationship between the frequency and the time period of the oscillation. Mathematically, it is given by :

Also, 
So,

The time taken to complete one oscillation is called the period of the oscillation and the number of oscillation is called the frequency if an oscillation.
Most likely, C. the Moon does not have a liquid core (this is what would create a magnetic field) is correct.
I hope this enough to help you!