Which of the following is a chemical change?

a. sulfur and iron filings are mixed together in a beaker at room temperature.

b. sulfur and iron filings are mixed together and the iron is removed with a magnet.

c. a mixture of sulfur and iron filings are heated until the contents glow red and the appearance of the mixture changes. a magnet can no longer remove iron filings.

d. a mixture of sulfur and iron filings are placed in carbon disulfide, the sulfur dissolves, leaving iron behind in the bottom of the beaker.