Which of the following is a physical change?
A. magnetzing an iron rod
B. roasting marshmallows on a campfire
c. milk souring
D. an antacid neutralizing stomach acid

plants need sunlight, water, and carbon dioxide to make food. plants use the raw materials of water, nutrients they absorb from soil, and carbon dioxide to make sugars the plant can use. energy from the sun and chlorophyll are also needed.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.