Which is a sign of chemical change A. Ice cream left at room temperature melts
B. Calcium chloride is dissolved in H2O and disappears
C. Paint on a freshly painted wall dries and is no longer sticky
D. When H2S gas is bubbled into a lead acetate solution a precipitate forms

Inside a flashbulb, oxygen surrounds a thin coil of magnesium. when the flashbulb is set off, a chemical reaction takes place in which magnesium combines with oxygen to form magnesium oxide. which of the chemical equations matches the reaction above? a. mg + o2 mgo2 + energy b. 2mg + o mg2o + energy c. 2mg + o2 2mgo + energy d. mg + o mgo + energy