the correct IUPAC name of the following compound `[Cr(NH_3)_5(NCS)][ZnCl_4]` is

Options

A. pentaammine isothicyanato chromium (III) tetra chlorozicate (II)
B. pentammine isothio cyanatezinc chloride chromate (III)
C. pentammine isothiocyanato chromate (II)
D. isothio cyanatopenta ammine chromium (II) zinc chloride(IV)

Answer

To determine the correct IUPAC name of the compound `[Cr(NH_3)_5(NCS)][ZnCl_4]`, we will follow these steps:

### Step 1: Identify the Components
The compound consists of two parts: a cation `[Cr(NH_3)_5(NCS)]` and an anion `[ZnCl_4]`.

### Step 2: Determine the Charge of the Anion
The anion `[ZnCl_4]` contains zinc (Zn) and four chloride ions (Cl). Zinc typically has a charge of +2, and each chloride ion has a charge of -1. Therefore, the total charge contributed by the four chloride ions is -4. Thus, the overall charge of the anion is:
\[ \text{Charge of Zn} (+2) + \text{Charge of 4 Cl} (-4) = -2 \]
This means the anion has a charge of -2.

### Step 3: Determine the Charge of the Cation
Since the overall compound is neutral, the cation must have a charge of +2 to balance the -2 charge of the anion.

### Step 4: Determine the Oxidation State of Chromium
Let the oxidation state of chromium (Cr) be \( x \). The ligands present are five ammonia (NH₃) molecules (which are neutral) and one isothiocyanate (NCS) ligand (which has a charge of -1). Therefore, we can set up the equation:
\[ x + 0 + (-1) = +2 \]
Solving for \( x \):
\[ x - 1 = 2 \implies x = +3 \]
Thus, chromium is in the +3 oxidation state.

### Step 5: Name the Cation
The cation `[Cr(NH_3)_5(NCS)]` contains:
- Five ammonia ligands (pentaammine)
- One isothiocyanate ligand (isothiocyanato)

In IUPAC naming, ligands are named in alphabetical order. Therefore, we write:
- Pentaammine
- Isothiocyanato

The name of the cation becomes:
\[ \text{Pentaammine isothiocyanato chromium(III)} \]

### Step 6: Name the Anion
The anion `[ZnCl_4]` contains four chloride ions. In IUPAC naming, we use the prefix "tetra" for four. The name of the anion becomes:
\[ \text{Tetrachlorido zinc(II)} \]

### Step 7: Combine the Names
Putting it all together, the full IUPAC name of the compound is:
\[ \text{Pentaammine isothiocyanato chromium(III) tetrachlorido zinc(II)} \]

### Final Answer
Thus, the correct IUPAC name of the compound `[Cr(NH_3)_5(NCS)][ZnCl_4]` is:
**Pentaammine isothiocyanato chromium(III) tetrachlorido zinc(II)**.

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