Across
1
Center of an atom or cell
5
Form of thermal energy
6
Smallest unit of an element
8
Magnetic metallic element
9
Infectious microscopic agent
10
Unit of heredity
Down
2
Curved glass that refracts light
3
Gas essential for breathing
4
Icy body with a tail near the sun
7
Preserved remains of ancient life
11
Substance with pH above 7
12
Gas form of a liquid