What do these two changes have in common? burning a marshmallow over a campfire milk going sour Select all that apply. Both are only physical changes. Both are chemical changes. Both are caused by heating. Both are caused by cooling.

## Step 1<br />The problem involves understanding the nature of two different changes: burning a marshmallow over a campfire and milk going sour. <br /><br />## Step 2<br />Burning a marshmallow over a campfire is a chemical change. This is because the heat from the campfire causes the marshmallow to undergo a chemical reaction, which changes its composition. The marshmallow's sugars and other organic compounds react with the oxygen in the air, producing new substances such as carbon dioxide and water vapor.<br /><br />## Step 3<br />Milk going sour is also a chemical change. This is because the bacteria in the milk consume the lactose (milk sugar) and produce lactic acid. This change in the chemical composition of the milk is what causes it to sour.<br /><br />## Step 4<br />Neither of these changes are physical changes. Physical changes involve a change in the physical properties of a substance, such as its shape or state, but not its chemical composition.<br /><br />## Step 5<br />Neither of these changes are caused by cooling. Both changes are caused by heating. The marshmallow is heated by the campfire, and the milk is heated by the bacteria.