Across
1
Gas essential for breathing
3
Second lightest element
5
Chemical element in table salt
6
Substance with pH above 7
9
Particle of light
10
Substance with pH below 7
11
Form of thermal energy
Down
1
Path of a planet around the sun
2
Blocking of light by a celestial body
4
Force that attracts objects together
7
Fourth state of matter
8
Element found in all living things