Answer:
'Oxidation states have changed.'
Explanation:
Redox Reactions can be identifiable by a change in oxidation number/states of two of the atoms in the reaction. Any reaction in which no oxidation numbers/state change is not a redox reaction.
It is a physical property because you aren't changing the actual thing, you are just changing its size. A chemical property is changing the arrangements of the atom to give you a totally new substance that cant be changed into its original form.<span />
It becomes gas because when the comet nears the sun, the sun freezes the comet causing it to become gas.