The logarithm from my understanding can never be negative. You can check this on a calculator. You may have a negative if it is shown as -(log x).
According to Raoult's law, Vapor pressure is directly proportional to the mole fraction of the solution. As 1.0 M CaF2 has least moles here, it has lowest vapor pressure.
In short, Your Answer would be Option D
Hope this helps!
Ni (Nickel) is the best conductor, and in fact the only conductor, in that list
