Across
1
Mass per unit volume
5
Icy body with a tail near the sun
6
Substance with pH below 7
7
Smallest unit of an element
8
Molten rock beneath Earth surface
9
Curved glass that refracts light
10
Unit of heredity
Down
2
Compound containing oxygen
3
Center of an atom or cell
4
Force that attracts objects together
11
Our home planet
12
Disturbance that transfers energy