Answer: Option (d) is the correct answer.
Step-by-step explanation:
A metal which has the largest size and the most valence electrons would have the highest conductivity because the larger is the size of a metal the more freely electrons can move in it. Hence, the metal can conduct electricity.
If the atom is smaller in size then the electrons will be tightly held around the nucleus and hence they won't be able to move freely. Therefore, they will not conduct electricity.
Thus, we can conclude that the atom with the largest radius and the most valence electrons would have the highest conductivity.