Across
1
Blocking of light by a celestial body
4
Smallest unit of an element
7
Substance with pH above 7
9
Chemical element in table salt
10
Mass per unit volume
Down
2
Gas form of a liquid
3
Unit of force
5
Preserved remains of ancient life
6
Gas essential for breathing
8
Tissue that contracts for movement
11
Amplified beam of light
12
Molten rock beneath Earth surface
13
Group of similar cells