Answer:
It was frozen.
Step-by-step explanation:
A substance may undergo any chemical change in its nature in all the given cases except when it is frozen.
A) during heating there is chances that it undergoes decomposition . Like if calcium carbonate is heated it converts to calcium oxide and carbon dioxide.
B) When a compound is hit with a hammer there is chance of its chemical decomposition.
C) If a compound is placed in a salt solution it may react with the salt or water.
D) However freezing is purely a physical process, where contact with any other compound or any chance of chemical decomposition is not possible.