9. At 25°C, which of the following substance has an standard enthalpy of formation equal to zero ?
(A)O2(g)
(B)H2O(g)
(C)CH4(g)
(D)CI(g)
(E)CO(g)

答案：登入後查看
統計： A(0), B(1), C(0), D(2), E(0) #2788657