What of these processes is a chemical change, not a physical change? 1. the burning of a match 2. the boiling of mercury 3. the dissolving of salt in water 4. melting ice 5. the breaking of a pencil?

A chemical change is one where the compounds are modified: a compound decomposes into its elements, or combine with other elements to form a different compound.

That is what happens when a match burns: oxygen reacts with the match compounds and form CO2(g), H2O(g) and other compounds depending on the composition of the match.

The other processes only involve a physical change of the compounds, but they remain being the same compounds (same elements with the same bonds).

Answser: option 1. the burning of a match.

Cr(oh)3 -> cr(3+) + 3oh-

Ithink is d. physical property