Which best describes a compound such as magnesium oxidea. an impure substance that is made up of two elementsb. a mixture of two uncommon substancesc. a mixture of two common elementsd. a pure substance that is made up of different elements

D. a pure substance that is made up of different elements

Step-by-step explanation:

There are two types of pure substances: elements and compounds.

Elements are made up of only one type of atom. And compounds are pure substances, that are made up of more than one type of element. Like - magnesium oxide. It is a compound of a metal with a non-metal and is held together with ionic bonds.

1) c 2143.6 cm

2) c 113.0 m

3) a 33.5 ft

4)   d 2 cm

5) c 20 mm

6) 180 in

7) d 120 ft