<span>Elements must be heated before they emit colored light because the heat being added to the elements will allow for a reaction to happen between the element and the oxygen in air. They are endothermic reactions where energy is needed in order for the reaction to proceed.</span>
Ba! It is a metal and wants to lose 2 electrons ASAP
Answer:the quality or character of being periodic; the tendency to recur at intervals.
"the periodicity of the sunspot cycle"
Explanation: