An unknown molecule substance x is added to a container of water, but will not dissolve in the water. substance x if therefore a. a polar molecule b. a nonpolar molecule c. there is not enough information to make a prediction on the polarity of substance x

 B. a nonpolar molecule 

Water is a molecule made of two hydrogens and one oxygen. Water structure looks like a mickey mouse which makes it polar. 
A polar compound will attract others polar molecules. That cause a polar substance will have much more solubility in water than non-polar substance like oil. Since the substance is not dissolved in water, it is more likely for it to be a non-polar molecule.