According to C.F.T, attraction between the central metal ion and ligands in a complex is purely electrostatic. The transition metal which forms the central atom cation in the complex is regarded as a positive ion. It is surrounded by negative ligands or neutral molecules which have a lone apir of electrons, if the ligand is a neutral molecule such as `NH_(3)`, the negative and of the dipole in the molecule is directed towards the metal cation. the electrons on the central metal ion are under repulsive forces from those on the ligands. thus the electrons occupy the d-orbitals remain away from the direction of approach ligands. ltBrgt Q. The value of 'x' in the complex `H_(x)[Co(CO)_(4)]` (on the basis of EAN rule), and geometry arround Co ion respectively is:

Options

A. 1, square planar
B. 2, tetrahedral
C. 1, tetrahedral
D. 2, square planar

Answer

To solve the question regarding the complex \( H_x[Co(CO)_4] \), we will follow a systematic approach based on the Effective Atomic Number (EAN) rule and the geometry around the cobalt ion.

### Step-by-Step Solution:

1. **Identify the Coordination Complex**:
The given complex is \( H_x[Co(CO)_4] \). Here, \( CO \) is a neutral ligand and cobalt (Co) is the central metal ion.

2. **Determine the Oxidation State of Cobalt**:
The overall charge of the complex can be expressed as:
\[ \text{Charge of complex} = \text{Charge of cobalt} + \text{Charge from ligands} \]
The ligands \( CO \) are neutral, contributing 0 charge. Thus, the charge of the complex is \( -x \) (from \( H_x \)). Let the oxidation state of cobalt be \( R \). Therefore, we have:
\[ -x = R + 0 \implies R = -x \]

3. **Calculate the Effective Atomic Number (EAN)**:
The formula for EAN is given by:
\[ \text{EAN} = Z + n - R \]
where \( Z \) is the atomic number of cobalt (27), \( n \) is the number of electrons donated by the ligands, and \( R \) is the oxidation state of the metal.

Since there are 4 \( CO \) ligands, each donating 2 electrons, we have:
\[ n = 4 \times 2 = 8 \]

4. **Set EAN Equal to the Nearest Noble Gas Atomic Number**:
The nearest noble gas to cobalt is krypton, which has an atomic number of 36. Therefore, we set up the equation:
\[ 36 = 27 + 8 - R \]

5. **Substituting the Oxidation State**:
Substitute \( R = -x \) into the EAN equation:
\[ 36 = 27 + 8 - (-x) \]
Simplifying this gives:
\[ 36 = 27 + 8 + x \]
\[ 36 = 35 + x \implies x = 1 \]

6. **Determine the Geometry Around the Cobalt Ion**:
The geometry of the complex can be determined by the hybridization of the cobalt ion. Given that \( CO \) is a strong field ligand, it will cause pairing of electrons in the d-orbitals. The hybridization for 4 ligands is \( sp^3 \), which corresponds to a tetrahedral geometry.

### Final Answer:
- The value of \( x \) in the complex \( H_x[Co(CO)_4] \) is **1**.
- The geometry around the Co ion is **tetrahedral**.