Total number of angle in `SeCl_(4)` which are less than `90^(@)`.

Explanation

To find the total number of angles in SeCl₄ that are less than 90°, we can follow these steps:

### Step 1: Determine the Valence Electrons
Selenium (Se) is in group 16 of the periodic table, so it has 6 valence electrons. Each chlorine (Cl) contributes 1 electron, and since there are 4 chlorine atoms, they contribute a total of 4 electrons.

**Calculation:**
- Valence electrons from Se: 6
- Valence electrons from 4 Cl: 4 × 1 = 4
- Total valence electrons = 6 + 4 = 10

### Step 2: Draw the Lewis Structure
In SeCl₄, selenium forms 4 single bonds with 4 chlorine atoms. After forming these bonds, selenium will have one lone pair of electrons remaining.

### Step 3: Determine the Steric Number
The steric number is calculated by adding the number of sigma bonds and the number of lone pairs:
- Number of sigma bonds = 4 (one for each Se-Cl bond)
- Number of lone pairs = 1

**Steric Number Calculation:**
Steric number = Number of sigma bonds + Number of lone pairs = 4 + 1 = 5

### Step 4: Determine the Hybridization
With a steric number of 5, the hybridization of Se in SeCl₄ is sp³d, which corresponds to a trigonal bipyramidal geometry.

### Step 5: Identify the Bond Angles
In a trigonal bipyramidal geometry, the bond angles are:
- 120° between the equatorial positions
- 90° between the axial and equatorial positions

### Step 6: Analyze the Effect of Lone Pairs
The presence of the lone pair affects the bond angles due to lone pair-bond pair repulsion. The lone pair will occupy one of the equatorial positions, which will cause the bond angles between the chlorine atoms to be less than the ideal angles.

### Step 7: Count the Angles Less Than 90°
In SeCl₄, the angles between the chlorine atoms that are affected by the lone pair will be less than 90°. The angles that are less than 90° are:
1. Between Cl1 and Cl2 (equatorial)
2. Between Cl1 and Cl3 (equatorial)
3. Between Cl2 and Cl4 (equatorial)
4. Between Cl3 and Cl4 (axial)

Thus, there are **4 angles** in SeCl₄ that are less than 90°.

### Final Answer
The total number of angles in SeCl₄ that are less than 90° is **4**.

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