The compound `K_(3)[Co(ONO)_(6)]` is called

Options

A. potassium cobaltinitrite
B. Fischer's salt
C. potassium hexanitritocobaltate (III)
D. potassium cobalt nitrate

Answer

To determine the name of the compound \( K_3[Co(ONO)_6] \), we will follow a systematic approach to naming coordination compounds.

### Step-by-Step Solution:

1. **Identify the Components**:
- The compound consists of potassium ions (K\(^+\)) and a coordination complex \([Co(ONO)_6]^{3-}\).
- The coordination complex contains cobalt (Co) and six nitrito ligands (ONO).

2. **Determine the Charge of the Coordination Sphere**:
- Potassium (K) has a +1 charge. Since there are three potassium ions, the total positive charge contributed by potassium is \( +3 \).
- The overall charge of the coordination compound is neutral, so the charge of the coordination sphere must be \( -3 \) to balance the +3 from potassium.

3. **Identify the Ligands**:
- The ligand here is nitrito, which is derived from nitrite (NO\(_2^-\)). Since the bonding occurs through the oxygen atom, we refer to it as "nitrito-O".

4. **Count the Ligands**:
- There are six nitrito ligands. In coordination chemistry, when there are six identical ligands, we use the prefix "hexa".

5. **Determine the Oxidation State of Cobalt**:
- Let the oxidation state of cobalt be \( x \).
- The equation for the charge balance in the coordination sphere is:
\[ x + 6(-1) = -3 \]
\[ x - 6 = -3 \implies x = +3 \]
- Thus, cobalt is in the +3 oxidation state.

6. **Construct the IUPAC Name**:
- The IUPAC name is constructed as follows:
- Name the ligands first in alphabetical order, followed by the metal with its oxidation state in Roman numerals.
- The name will be: **Potassium hexanitrito-O-cobaltate(III)**.

7. **Common Name**:
- The compound is also commonly known as **Fischer's salt**.

### Final Answer:
The compound \( K_3[Co(ONO)_6] \) is called **Potassium hexanitrito-O-cobaltate(III)** or commonly known as **Fischer's salt**.