Which one of the following is called green vitriol?

Green vitriol is the common name for ferrous sulfate \((FeSO_4)\). It is a greenish crystalline solid that is often found as a heptahydrate \((FeSO_4·7H_2O)\) with seven water molecules associated with each \(FeSO_4\) unit. Green vitriol is also known as iron(II) sulfate or copperas and has various industrial uses, including as a precursor for the production of other iron compounds, in water treatment, and as a fertilizer in agriculture.