Which of the following is an oxidation-reduction reaction? zns(s) + 2o2(g) mc011-1.jpg znso4(s) cao(s) + h2o(l) mc011-2.jpg ca(oh)2(s) 6li2o(s) + p4o10(g) mc011-3.jpg 4li3po4(s) so2(g) + h2o(l) mc011-4.jpg h2so3(aq)

Which of the following is an indication that a substance has undergone a chemical change? a. no new product has been formed. b. the color of the substance has not changed. c. the original constitute has not changed. d. the molecular structure has changed.