The oxidation number of Co in \([Co(en)_3]_2(SO_4)_3\) is

+3

The correct answer is option 3. \(+3\)

The oxidation number of Co in \([Co(en)_3]_2(SO_4)_3\) is 3.

The oxidation number of a metal ion in a coordination complex is calculated by adding the oxidation numbers of the ligands and subtracting the overall charge of the complex. In this case, the ligands are ethylenediamine (en), which has an oxidation number of 0, and sulfate (SO₄), which has an oxidation number of -2. The overall charge of the complex is 0. So, the oxidation number of Co can be calculated as follows:

Let us assume the oxidation number of \(Co\) be \(\)x

\(2(x + 0) + 3(-2) = 0\)

\(⇒ 2x - 6 =0\)

\(⇒ 2x = 6\)

\(⇒ x = +3\)