Which of the following is a correct statement ?

Options

A. `CO_(2)` is a monomer while `SiO_(2)` is a three dimensional giant molecule
B. Graphite is a nonconductor of electricity
C. In `(CH_(3))_(3) , C-N-C` bond angle is approximately `107^(@)` whereas in `(SiH_(3))_(3)` N , `Si-N-Si` bond angle is approximately `120^(@)`
D. In `CO_(3)^(2-)` ion all C-O bonds are equal , while in `H_(2)CO_(3)` all C-O bonds are not equal

Answer

To determine which of the statements is correct, we will analyze each statement one by one.

### Step 1: Analyze the First Statement
**Statement:** CO2 is a monomer while SiO2 is a three-dimensional GENT molecule.

- **CO2 Structure:** Carbon dioxide (CO2) has a linear structure due to its two double bonds with oxygen. It is indeed a monomer because it exists as individual molecules.
- **SiO2 Structure:** Silicon dioxide (SiO2) forms a three-dimensional network structure (often referred to as a giant covalent structure) due to the extensive bonding between silicon and oxygen atoms.

**Conclusion:** The first statement is correct.

### Step 2: Analyze the Second Statement
**Statement:** Graphite is a non-conductor of electricity.

- **Graphite Structure:** Graphite has a layered structure with delocalized electrons that can move freely between layers. This property allows graphite to conduct electricity.

**Conclusion:** The second statement is incorrect.

### Step 3: Analyze the Third Statement
**Statement:** In CH3 thrice N, the bond angle is approximately 107°, while in SiH3N, the Si-N-Si bond angle is approximately 120°.

- **CH3 thrice N Structure:** The nitrogen atom in trimethylamine (CH3)3N has a lone pair, which slightly reduces the bond angle from the ideal tetrahedral angle (109.5°) to about 107° due to lone pair-bond pair repulsion.
- **SiH3N Structure:** In SiH3N, the presence of a lone pair on nitrogen and the higher electronegativity of silicon compared to nitrogen leads to a trigonal planar arrangement around silicon, resulting in a bond angle of approximately 120°.

**Conclusion:** The third statement is correct.

### Step 4: Analyze the Fourth Statement
**Statement:** In CO3 2-, all CO bonds are equal, whereas in H2CO3, the bond angles are not equal.

- **CO3 2- Structure:** The carbonate ion (CO3 2-) exhibits resonance, meaning that the double bond can be delocalized among the three oxygen atoms. This results in all C-O bonds being equivalent.
- **H2CO3 Structure:** In carbonic acid (H2CO3), there is no resonance stabilization to equalize the bond angles, leading to unequal bond angles.

**Conclusion:** The fourth statement is also correct.

### Final Summary
- The correct statements are:
- First statement (CO2 is a monomer and SiO2 is a three-dimensional GENT molecule) is correct.
- Third statement (bond angles in CH3 thrice N and SiH3N) is correct.
- Fourth statement (CO3 2- and H2CO3 bond characteristics) is correct.

### Correct Statements:
1. CO2 is a monomer while SiO2 is a three-dimensional GENT molecule.
2. In CH3 thrice N, the bond angle is approximately 107°, while in SiH3N, the Si-N-Si bond angle is approximately 120°.
3. In CO3 2-, all CO bonds are equal, whereas in H2CO3, the bond angles are not equal.