Across
1
Precious yellow metallic element
3
Positive particle in nucleus
4
Biological catalyst
7
Center of an atom or cell
8
Icy body with a tail near the sun
9
Substance with pH above 7
10
Natural satellite of Earth
Down
2
Reddish electrical conductor
5
Absolute temperature scale unit
6
Naturally occurring inorganic solid
11
Path of a planet around the sun
12
Fourth state of matter
13
Our home planet