Coal consists of nearly pure carbon, an element. When coal burns in air, it combines with the element oxygen from the air. Which of the following best describes the product of burning coal?

A. water, a heterogeneous mixture of atoms of hydrogen and oxygen
B. carbon dioxide, a heterogeneous mixture of atoms of carbon and oxygen
C. carbon dioxide, a homogeneous mixture of atoms of carbon gas and oxygen gas
D. carbon dioxide, a compound of atoms of carbon and oxygen

Astudent pours 10.0 g of salt into a container of water and observes the amount of time it takes for the salt to dissolve. she then repeats the process using the same amounts of salt and water but this time she slowly stirs the mixture while it is dissolving. the student performs the experiment one more time but this time she stirs the mixture rapidly. the dependent variable in this experiment is: time for salt to dissolve speed of stirring amount of water mass of salt