Answer
a. chemical change;
b. physical change;
c. physical change;
d. chemical change
Work Step by Step
When sugar burns, it reacts with oxygen and undergoes a combustion reaction and converts the sugar to carbon dioxide and water (in the form of gas). This essentially changes the sugar's composition.
Sugar dissolving in water will just change sugar's physical state. The sugar is the same composition as it was before it was dissolved in water.
When the platinum ring become dull, this is a change in physical appearance. Hence, this is a physical change.Exposure to air will lead to silver undergoing oxidation. This is a chemical change.
