Across
1
Hottest planet in solar system
5
Smallest unit of an element
6
Ball of burning gas in space
7
Unit of force
12
Substance with pH below 7
13
Biological catalyst
Down
2
Tissue that contracts for movement
3
Nerve cell in the brain
4
Chemical element in table salt
8
Curved glass that refracts light
9
Positive particle in nucleus
10
Reddish electrical conductor
11
Particle of light