The enthalpy change change for which reaction represents the standard enthalpy of formation for hydrogen cyanide, HCN?

Options

A. `H(g)+C_("graphite")+N(g)to HCN(g)`
B. `(1)/(2)H_(2)(g)+C_("graphite")(1)/(2)N_(2)(g) to HCN(g)`
C. `HCN(g)to (1)/(2)H_(2)(g)+C_("graphite")+(1)/(2)N_(2)(g)`
D. `H_(2)(g)+2C_("graphite")+N_(2)(g)to2HCn(g)`

Answer

b