Across
1
Hottest planet in solar system
3
Our home planet
6
Nerve cell in the brain
7
Unit of heredity
8
Particle of light
10
Force that attracts objects together
11
Fourth state of matter
Down
2
Form of thermal energy
4
Gas essential for breathing
5
Center of an atom or cell
9
Substance with pH above 7
12
Precious yellow metallic element