Oxidation number of Al(OH)4

Explanation:

The sum of all oxidation numbers in a neutral compound is zero. The sum of all oxidation numbers in a polyatomic (many-atom) ion is equal to the charge on the ion. The oxidation number of oxygen in a compound is usually –2. The oxidation state of hydrogen in a compound is usually +1.

The oxidation state of Al in Al(OH)

4

−

x+4(+1−2)=−1

∴x=+3

The oxidation state of Mn in MnO

2

y+2(−2)=0

∴y=+4

thank u

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.