The correct answer is a) burning sugar.
When sugar is burned, it undergoes a chemical change. This process involves the sugar reacting with oxygen in the air, resulting in the formation of new substances – primarily carbon dioxide, water vapor, and ash. The original chemical structure of the sugar is altered, making this a clear example of a chemical change.
In contrast, making a snowman involves physical changes, such as packing snow together, and bending a steel rod is also a physical change, as the steel retains its original properties and structure even after being bent. Therefore, only burning sugar constitutes a chemical change.