\(\begin{array}{l} a)\\ n{O_2} = \dfrac{{6,72}}{{22,4}} = 0,3\,mol\\ b)\\ 2{C_2}{H_6} + 7{O_2} \to 4C{O_2} + 6{H_2}O\\ c)\\ nC{O_2} = \dfrac{{0,3 \times 4}}{7} = \dfrac{6}{{35}}\,mol\\ n{H_2}O = \dfrac{{0,3 \times 6}}{7} = \dfrac{9}{{35}}\,mol\\ \Rightarrow m{H_2}O = \dfrac{9}{{35}} \times 18 = 4,63g\\ d)\\ n{C_2}{H_6} = \dfrac{{0,3 \times 2}}{7} = \dfrac{3}{{35}}\,mol\\ m{C_2}{H_6} = \dfrac{3}{{35}} \times 30 = 2,57g \end{array}\)