N and N
N and H
O and Na
H and H
Extensive properties, such as mass and volume, depend on the amount of matter being measured. Intensive properties, such as density and color, do not depend on the amount of the substance present. Physical properties can be measured without changing a substance's chemical identity.
Tom's controlled plant should be placed in a room with no windows and at room temperature. This will keep both plants the same variables except for temperature.