The molar enthalpy of formation of pyridine(liquid), C4H5N, is +100.2KJ/mol.
a) Write the balanced equation for the formation of pyridine from its elements, that is, for the reaction for which the enthalpy of reaction is +100.2KJ.
b) Write the balanced equation for which the enthalpy change is +200.4KJ.

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Isn't the heat of formation of pyridine NEGATIVE? Isn't the heat of formation of pyridine a constant, regardless of synthetic route? Why is the heat of formation in your second option exactly twice the first one? Now I remember why I never liked Thermo.

The second question asks for the 'enthalpy change' not the standard enthalpy of formation :)

But yes, I'd expect that the enthalpy should be negative too... but according to wikipedia, the yield of this reaction is very low, so maybe it's really positive :(

Anyway, back to the question. Could you define the term enthalpy change of formation? The answer to your first question lies in this definition.