The of a compound is the amount change in enthalpy involved in the synthesis of 1 mole of a compound from its elements, with all substances in their standard states at 25°c.

a. enthalpy
b. heat of reaction
c. heat of solidification
d. standard heat of formation

I believe the correct answer would be the standard heat of formation. The keyword in the statement would be synthesis and standard state. Synthesis would always mean formation of something and standard states would mean at a temperature of 25 C and 1 atm pressure.

They lack magnetic fields i do believe

Cr(oh)3 -> cr(3+) + 3oh-