Which statement is true about physical changes and chemical changes? a. chemical changes are not observable. b. chemical changes always produce new substances. c. physical changes can change physical and chemical properties. d. physical and chemical changes cannot happen at the same time.

According to newton’s law of universal gravitation, which statements are true? as we move to higher altitudes, the force of gravity on us decreases. as we move to higher altitudes, the force of gravity on us increases. as we gain mass, the force of gravity on us decreases. as we gain mass, the force of gravity on us increases. as we move faster, the force of gravity on us increases.

Explain the difference in reactivity of the elements based on their electron configurations.

What is the answer to these problems 30 pt