Across
1
Second lightest element
4
Ball of burning gas in space
6
Substance with pH below 7
7
Biological catalyst
8
Disturbance that transfers energy
9
Reddish electrical conductor
10
Unit of force
11
Path of a planet around the sun
12
Naturally occurring inorganic solid
Down
2
Compound containing oxygen
3
Group of similar cells
5
Smallest unit of an element
9
Basic unit of life