Answer:
(a), (b) and (c)
Step-by-step explanation:
The standard Gibbs free energy of formation of a compound is defined as the change of Gibbs free energy that occurs in the formation of 1 mole of a substance from its component elements in their standard states.
Based on this definition, elements in their standard state have a standard free energy of formation of zero.
Standard state of aluminium is Al(s), of bromine is Br₂(l) and for mercury is Hg(l). That means the free energy of formation is zero for (a), (b) and c.
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