Elements in group via (group 16) have similar properties because they all have a. the same number of valance electrons. b. the same number of electrons needed to fill their octet. c. the same number of electrons shells. d. full octets

A

Explanation: Elements of group VIA have valence shell electronic configuration ns^2 np^4, they all have same number of valence electrons and have similar properties.

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.