Which of the following are true ?

Options

A. `He_(2) and BiCl_(5)` do not exist
B. There are two `p pi-d pi` bonds in `SO_(3)`
C. `SeF_(4) and CH_(4)` are tetrahedral
D. `I_(3)^(-)` is linear molecule with `sp^(3)d` hybridisation

Explanation

To determine which statements are true regarding the existence of certain molecules and their bonding characteristics, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Evaluate Helium-2 (He2):**
- Helium has an atomic number of 2, meaning it has 2 electrons. In a diatomic helium molecule (He2), there would be a total of 4 electrons.
- According to Molecular Orbital Theory (MOT), the electron configuration for He2 would be:
- σ(1s)² σ*(1s)²
- The bond order is calculated as:
\[ \text{Bond Order} = \frac{\text{Number of bonding electrons} - \text{Number of anti-bonding electrons}}{2} = \frac{2 - 2}{2} = 0 \]
- A bond order of 0 indicates that He2 does not exist.

2. **Evaluate Bismuth Chloride (BiCl5):**
- Bismuth (Bi) has an oxidation state of +5 in BiCl5. The electronic configuration of bismuth is [Xe] 6s² 6p³.
- The +5 oxidation state is less stable due to the inert pair effect, which suggests that the 6s electrons do not participate in bonding.
- Therefore, BiCl5 is not a stable compound and does not exist.

3. **Evaluate the Bonding in SO3:**
- Sulfur (S) has 6 valence electrons. In SO3, sulfur can undergo hybridization to form three bonds with oxygen.
- The hybridization involves the promotion of electrons to higher energy orbitals, leading to the formation of bonds.
- SO3 has two pi bonds and one sigma bond, which can be described as having p-d hybridization.
- Thus, the statement about SO3 having two p-d bonds is correct.

4. **Evaluate the Geometry of SCF4 and CH4:**
- SCF4 has a total steric number of 5 (4 bonding pairs and 1 lone pair), leading to sp³d hybridization and a trigonal bipyramidal geometry.
- CH4 has a steric number of 4 (4 bonding pairs and 0 lone pairs), leading to sp³ hybridization and a tetrahedral geometry.
- The shapes differ due to the presence of a lone pair in SCF4, making its shape see-saw rather than tetrahedral.

5. **Evaluate the Geometry of I3-:**
- Iodine (I) has 7 valence electrons, and with an additional negative charge, it has 8 valence electrons.
- I3- has a total steric number of 5 (2 bonding pairs and 3 lone pairs), leading to sp³d hybridization and a trigonal bipyramidal geometry.
- However, the presence of three lone pairs results in a linear shape for I3-.

### Conclusion:
Based on the analysis:
- **True Statements:**
- Helium-2 does not exist.
- Bismuth Chloride (BiCl5) does not exist.
- SO3 has two p-d bonds.
- I3- is a linear molecule with sp³d hybridization.