Answer: c. no new substance is formed.
Explanation:
A physical change is defined as a change in which there is alteration in shape, size etc. No new substance gets formed in these reactions.
Example: Melting of ice
\(H_2O(s)\righarrow H_2O(l)\)
A chemical change is defined as a change in which a change in chemical composition takes place. A new substance is formed in these reactions. Chemical reactions are usually characterized by change in color, heat change, precipitate formation and evolution of bubbles.
Example: Oxidation of magnesium
\(2Mg+O_2\rightarrow 2MgO\)
