Which of the following is a property of metals that is due to the delocalized electrons
a. transparency
b. dull appearance
c. brittle
d. good conductor

Good conductor

Explanation:

Metals form metallic bonds. They are also sometimes called 'a sea of electrons'. Basically, metal cations are surrounded by a sea of closely packed valence electrons. This close packing lets the particles of a metal interact much more efficiently and transfer heat or electric current efficiently. The valence electrons and metals ions are also moving to some extent, so besides being packed efficiently, they can also interact and collide to transfer electricity and heat.

This makes metals good heat and electric conductors.

the answer would be c

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)