Which of the following are the weakest conductors?

A) alkaline earth metals

B) alkali metals

C) metalloids

D) metals

C) metalloids

Explanation:

Metalloids have some of the properties of metals and some of nonmetals.

Their ability to conduct heat is between that of metals (good) and nonmetals (poor).

They can usually conduct electricity only at high temperatures.

A), B) and D) are wrong. Alkali, alkaline earth, and transition metals are good conductors of heat and electricity.