Across
1
Gas essential for breathing
5
Tectonic landmass section
6
Unit of power
7
Second lightest element
10
Unit of energy
12
Fourth state of matter
Down
2
Biological catalyst
3
Icy body with a tail near the sun
4
Our home planet
8
Basic unit of life
9
Amplified beam of light
11
Substance with pH below 7
12
Positive particle in nucleus