The reason for the distinct difference in the properties of `CO_2 and SiO_2` is

Options

A. Carbon is more electronegative than O and in case of `SiO_2` oxygen is more electronegative than silicon
B. Carbon has small size and forms a `pi` bond with good overlap whereas silicon has larger size hence has a poor `pi` - overlap
C. First ionization potential of carbon is higher than that of silicon
D. Carbon has only 'p' orbitals and lacks 'd' orbitals whereas silicon has 'd' orbitals

Answer

To determine the reason for the distinct difference in the properties of carbon dioxide (CO₂) and silicon dioxide (SiO₂), we can analyze the bonding and structural characteristics of both compounds. Here’s a step-by-step solution:

### Step 1: Understand the Molecular Structure
- **Carbon Dioxide (CO₂)**: CO₂ is a linear molecule with a double bond between carbon and each oxygen atom. The carbon atom is sp hybridized, and the oxygen atoms are sp² hybridized.
- **Silicon Dioxide (SiO₂)**: SiO₂ has a three-dimensional lattice structure where each silicon atom is covalently bonded to four oxygen atoms in a tetrahedral arrangement. There are only single bonds present.

**Hint**: Consider how the hybridization of the central atom affects the type of bonds formed in each molecule.

### Step 2: Compare Atomic Sizes
- Carbon (C) has a smaller atomic radius compared to silicon (Si). This smaller size allows for better overlap of p-orbitals, which is crucial for the formation of pi bonds.
- Silicon, being larger, has poorer overlap with oxygen's p-orbitals, leading to the absence of pi bonding.

**Hint**: Think about how atomic size influences the ability of atoms to form multiple bonds.

### Step 3: Analyze Bonding Types
- In CO₂, the effective overlap of the p-orbitals between carbon and oxygen leads to the formation of strong pi bonds, making CO₂ a gas at room temperature.
- In SiO₂, the lack of pi bonding due to poor overlap results in a network solid structure, making SiO₂ a solid at room temperature.

**Hint**: Reflect on how the type of bonding affects the physical state of the substance.

### Step 4: Evaluate Electronegativity and Orbital Availability
- While electronegativity plays a role in bonding, it is not the primary reason for the distinct properties of CO₂ and SiO₂. Oxygen is more electronegative than both carbon and silicon.
- Carbon has only p-orbitals available for bonding, while silicon has d-orbitals that can participate in bonding, but this is not the main reason for the difference in properties.

**Hint**: Consider how the presence of different types of orbitals can influence bonding but focus on the primary factors.

### Conclusion
The distinct difference in the properties of CO₂ and SiO₂ primarily arises from the ability of carbon to form pi bonds due to its smaller size and effective orbital overlap, while silicon's larger size prevents such bonding, leading to a solid structure for SiO₂.

**Final Answer**: The correct option is **Option 2**: Carbon has a small size and forms pi bonds with good overlap, whereas silicon has a larger size and hence has poor pi overlap.