Across
1
Precious yellow metallic element
3
Second lightest element
4
Basic unit of life
6
Smallest unit of an element
9
Ball of burning gas in space
10
Center of an atom or cell
Down
2
Blocking of light by a celestial body
5
Measure of matter in an object
7
Preserved remains of ancient life
8
Unit of energy
11
Positive particle in nucleus
12
The Red Planet