Answer
A. helium -> single atoms
B. $CCl_4$ -> molecules
C. $K_2SO_4$ -> formula units
D. bromine -> diatomic molecules
Work Step by Step
Bromide is diatomic, meaning its atoms naturally bond with itself to form molecules. $CCl_4$ is a molecule, where different types of atoms bond together covalently. $K_2SO_4$ represents a formula unit, the lowest whole number ratio of ions in a compound.