Comparison of Size of SO3, NO3-, CO32-, and COCl2

Introduction
In this response, we will compare the sizes of the molecules SO3, NO3-, CO32-, and COCl2. The size of a molecule is influenced by various factors, including the number of atoms, the type of bonding, and the presence of lone pairs of electrons. We will consider these factors to determine the relative sizes of the given molecules.

Factors Affecting Size
1. Number of Atoms: Generally, as the number of atoms in a molecule increases, the size of the molecule also increases.
2. Type of Bonding: The presence of multiple bonds, such as double or triple bonds, can lead to a more compact molecular structure, reducing the overall size of the molecule.
3. Lone Pairs of Electrons: Lone pairs of electrons can cause repulsion, resulting in a larger molecular size.

Comparison of Sizes
1. SO3 (Sulfur Trioxide): Sulfur trioxide consists of one sulfur atom and three oxygen atoms. It has a trigonal planar molecular geometry due to the presence of three double bonds between the sulfur and oxygen atoms. The absence of lone pairs and the compact structure make SO3 relatively smaller in size.

2. NO3- (Nitrate): Nitrate ion contains one nitrogen atom and three oxygen atoms. The nitrogen atom is bonded to three oxygen atoms through single bonds, and it also possesses a lone pair of electrons. The presence of a lone pair of electrons leads to electron-electron repulsion, causing the molecule to be larger in size compared to SO3.

3. CO32- (Carbonate): Carbonate ion consists of one carbon atom and three oxygen atoms. The carbon atom is bonded to three oxygen atoms through single bonds, and it has no lone pairs of electrons. The absence of lone pairs and the molecular structure with single bonds make CO32- larger in size compared to both SO3 and NO3-.

4. COCl2 (Phosgene): Phosgene is a molecule with one carbon atom, one oxygen atom, and two chlorine atoms. The carbon atom is bonded to the oxygen atom through a double bond and to the chlorine atoms through single bonds. It has no lone pairs of electrons. The presence of double bonding and the absence of lone pairs make COCl2 smaller in size compared to CO32-.

Conclusion
In conclusion, the relative sizes of the given molecules are as follows:
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