Which of the following sentences represents a physical change? sugar dissolves in coffee iron rusts gasoline burns in an engine a candle burns

The sentence that represents a physical change is sugar dissolves in coffee.
The reason why this is a physical, and not a chemical change is because the sugar completely changed its state - it used to be solid, but then it melted into the coffee and became liquid.
The other options are all chemical changes. 

Because a model would make the investigation easier to understand