When two substances are mixed together, a color change is observed. does this mean that a chemical reaction has definitely occurred? - yes because any change indicates a chemical reaction. - no because some physical changes produce color changes. - no because color changes are not indicators of chemical reactions. - yes because color changes occur only when new compounds are formed.

 No because some physical changes produce color changes.

Explanation:-

A physical reaction is defined as the reaction in which a change in shape, size takes place. No new substance gets formed in these reactions.

Example: Addition of food colors to water is a physical process and lead to color change

A chemical reaction is defined as the reaction in which a change in chemical composition takes place. A new substance is formed in these reactions.

Example: Oxidation of magnesium leads to formation of white magnesium oxide and is a chemical change.

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6