Which of the following gases is not found in earth’s atmosphere? a. oxygen c. hydrogen b. nitrogen d. all of the above are in the atmosphere

Compare and contrast physical changes with chemical changes.

Three cards with holes are arranged in a straight line. a light is shined through the first card’s hole and travels through all three cards. what does this tell you about light rays? a) that light is reflected b) that light is refractive c) that light travels in a straight line d) that light does not travel in a straight line

Is a chemical message sent by another individual.