If two substances combine to form a new substance with different properties it is called

The answer to your question is Compound

Explanation:

A Compound is a mixture of two or more elements that when combine gives to the new substance different properties from the original elements.

Examples of compounds

                    Elements                           Compounds

               Hydrogen   +   Oxygen   ⇒    Water

               Sodium       +   Chlorine  ⇒    Sodium Chloride

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8