Across
1
Fourth state of matter
3
Mass per unit volume
4
Icy body with a tail near the sun
5
Center of an atom or cell
8
Gas essential for breathing
9
Chemical element in table salt
10
Nerve cell in the brain
Down
1
Glass that splits light into spectrum
2
Curved glass that refracts light
4
Element found in all living things
6
Hottest planet in solar system
7
Second lightest element
11
Substance with pH above 7
12
Blocking of light by a celestial body