Which of the following is true regarding a charged coordination entity?

The sign of the charge is written after the number

The correct answer is option 3. The sign of the charge is written after the number.

In coordination chemistry, when representing charged coordination entities, such as complex ions or coordination compounds, the sign of the charge is often written after the numerical value that represents the charge.

For example, consider the coordination complex \([Co(NH_3)_4Cl_2]^{2-}\). In this complex:

The numerical value "2" indicates the magnitude of the charge.

The "-" sign written after the numerical value indicates that the charge on the complex ion is negative.

This notation helps to clearly indicate the charge of the coordination entity and distinguish it from any counterions or other components in the compound. It's a convenient way to convey important information about the charge of the coordination complex while also maintaining clarity in the representation of the compound.

Therefore, option 3 is indeed a valid convention for representing the charge on a coordination entity: "The sign of the charge is written after the number."