To solve this problem, we need to determine the form in which iron is absorbed by plants.$\newline$Let's analyze the options:$\newline \bullet$Option 1: Free element$\newline$ - Iron is not absorbed by plants in its free elemental form.$\newline \bullet$Option 2: Ferrous$\newline$ - Ferrous iron $(Fe^{2+})$ is one of the forms in which iron can be absorbed by plants.$\newline \bullet$Option 3: Ferric$\newline$ - Ferric iron $(Fe^{3+})$ is another form in which iron can be absorbed by plants.$\newline \bullet$Option 4: Both ferric and ferrous$\newline$ - Plants can absorb iron in both ferrous $(Fe^{2+})$ and ferric $(Fe^{3+})$ forms, but the absorption efficiency and mechanism can vary.$\newline$In general, plants primarily absorb iron in the ferrous form $(Fe^{2+})$, but they can also take up ferric iron $(Fe^{3+})$ after it is reduced to the ferrous form.$\newline$Therefore, the correct answer is Option 3: Ferric.