Which of these is an example of a physical change?

Physical changes are anything that changes the subject physically (crinkling paper, turning ice into water, or cutting grass) without chemically altering the makeup of the substance (burning, rusting/oxidation, or digestion).

You could think of it as this way: physical changes can be reversed while chemical changes cannot be reversed.

8 carbon atoms forming single bonds with 18 hydrogen atoms; a triple bond exists between the third and fourth carbon atom from the right

explanation:

some sources quote the lethal dose, for an average 170lbs opiate-naive individual is between 75 and 375 mg