Which of these is an indication that a chemical reaction has occurred? a. the melting of a substance b. the boiling of a substance c. the formation of precipatation d the freezing of a substance & you!

Asingle atom of an element has 21 neutrons, 20 electrons, and 20 protons. which element is it? ok o z

What is the volume occupied by 10.0 dm3 of gas at standard pressure after it has been compressedat constant temputure to 500.0 kpa?

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