Across
1
Gas essential for breathing
4
Magnetic metallic element
5
Fourth state of matter
9
Push or pull on an object
11
Center of an atom or cell
Down
2
Smallest unit of an element
3
Particle of light
6
Biological catalyst
7
Tissue that contracts for movement
8
Mass per unit volume
10
Nerve cell in the brain
12
Hottest planet in solar system