Across
1
Curved glass that refracts light
3
Gas essential for breathing
7
Measure of matter in an object
8
Substance with pH below 7
9
Amplified beam of light
11
Center of an atom or cell
Down
2
Mass per unit volume
4
Biological catalyst
5
Blocking of light by a celestial body
6
Icy body with a tail near the sun
10
Magnetic metallic element
12
Chemical element in table salt