Give the symbol for stannic ion

May someone me with these science questions

The equation below shows a chemical reaction. a + b + heat —> c + d according to the law of conservation of energy, which statement is true? a. the reactants absorb heat because they have less energy than the products. b. the products release heat because they have more energy than the reactants. c. the reactants generate heat because they have more energy than the products. d. the products require heat to form because they have less energy than the reactants.

Based on the formulas, select the compounds below that are covalent: kbr sif4 al2o3 co2 naco3 s7o2 pcl3 fe3n2 h2o s2f10