Correct statements among the following is/are
A) Absolute values of enthalpy cannot be determined
B) Heat of ionization of ${\text{H}}_{\text{aq}}^{+}$ is arbitrarily taken as zero
C) Enthalpy of a pure crystalline solid is zero at zero K
D) Standard enthalpy of formation of ${\text{H}}_{\text{2}}{\text{O}}_{\left(\mathrm{\ell }\right)}$ is zero