Across
1
Precious yellow metallic element
3
Curved glass that refracts light
4
Push or pull on an object
6
The Red Planet
7
Mass per unit volume
9
Center of an atom or cell
12
Substance with pH below 7
Down
2
Compound containing oxygen
4
Preserved remains of ancient life
5
Unit of energy
8
Ball of burning gas in space
10
Tectonic landmass section
11
Biological catalyst
13
Second lightest element