Across
1
Mass per unit volume
3
Unit of energy
6
Hottest planet in solar system
7
Particle of light
9
Substance with pH below 7
10
Molten rock beneath Earth surface
11
Measure of matter in an object
Down
2
Chemical element in table salt
4
Nerve cell in the brain
5
Smallest unit of an element
8
Icy body with a tail near the sun