Molecules are different from atoms because they
a) have less energy
b) are much smaller
c) have unique properties
d) contain chemical bonds

Option (D) is the correct answer.

Explanation:

Molecules are defined as the substances which contain same type of elements which are chemically combined to each other.

For example, is a molecule which contains two same atoms that is, chlorine atoms.

In this molecule, the atoms are chemically combined together due to sharing of electrons. Hence, they tend to form covalent bonds.

Therefore, we can conclude that molecules are different from atoms because they contain chemical bonds.

1. 1 mole of anything contains 6.022x10^23 pieces  

d  

2. a  

3. c, number  

5. 1.24x10^24atoms / 6.022x10^23atoms/mole = 2moles h2 atoms  

6. fe2br3 mass = 2moles x mass fe + 3 moles x mass br  

molar mass = grams / number of moles = g/mole  

to find moles = g / molar mass  

to find mass = g = molar mass / moles

58750.08068 is the answer i think