Human induced environmental changes can affect living things at which levels?

What metric units would you use to measure the thickness of a key

The chemical equation below shows the reaction of sodium (na) and chlorine (cl) to form sodium chloride (nacl). 2na + cl2 → 2nacl in this equation, which of the following is a reactant? i. sodium ii. chlorine iii. sodium chloride

What is the most common reason for matter changing its state?