#CO_2#: Each carbon dioxide molecule is formed from 1 C atom and 2 O atoms. We know that C has 4 valence electrons and that O has 6 valence electrons, which means that the number of valence electrons for 1 #CO_2# molecule will be
#1 * 4 + 2 * 6 = 16e^-#
#H_2O#: Again, each water molecule is formed from 1 O atom and 2 H atoms. Since the number of valence electrons for O and H are 6 and 1, respectively, one molecule of water will have
#2 * 1 + 1 * 6 = 8# valence electroncs.
#H_2SO_4#: One molecule of sulfuric acid has 2 H atoms, 1 S atom, and 4 O atoms, each contributing 1, 6, and 6 valence electrons. So the number of valence electrons for 1 molecule of sulfuric acid is