Across
1
Gas essential for breathing
2
Smallest unit of an element
4
Push or pull on an object
7
Gas form of a liquid
9
Second lightest element
12
Positive particle in nucleus
Down
1
Path of a planet around the sun
3
Natural satellite of Earth
5
Mass per unit volume
6
Group of similar cells
8
Element found in all living things
10
The Red Planet
11
Our home planet