**Non-Ideal Solution**

A non-ideal solution is a mixture that does not obey Raoult's Law. Raoult's Law states that the vapor pressure of a component in an ideal solution is directly proportional to its mole fraction in the solution. When a solution deviates from Raoult's Law, it is considered a non-ideal solution.

**Pair 1: CCl4 and SiCl4**

- Both CCl4 (carbon tetrachloride) and SiCl4 (silicon tetrachloride) are nonpolar compounds.
- Nonpolar compounds tend to form ideal solutions with each other because they have similar intermolecular forces (Van der Waals forces).
- Since both CCl4 and SiCl4 have similar molecular structures and polarities, they are likely to form an ideal solution and not a non-ideal solution.

**Pair 2: C6H5Cl and C6H5Br**

- C6H5Cl (chlorobenzene) and C6H5Br (bromobenzene) are both organic compounds.
- Organic compounds can have different molecular structures and intermolecular forces.
- Chlorobenzene and bromobenzene have different molecular structures and polarities, which can lead to deviations from Raoult's Law.
- The difference in intermolecular forces between chlorobenzene and bromobenzene can cause the solution to be non-ideal.

**Pair 3: CHCl3 and CCl4**

- CHCl3 (chloroform) and CCl4 (carbon tetrachloride) are both chlorinated organic compounds.
- Both compounds have similar molecular structures and polarities, which are important factors for ideal solution formation.
- The similarity in intermolecular forces between CHCl3 and CCl4 suggests that they are likely to form an ideal solution rather than a non-ideal solution.

**Pair 4: C6H6 and toluene**

- C6H6 (benzene) and toluene (methylbenzene) are both aromatic hydrocarbons.
- These compounds have similar molecular structures, but toluene has an additional methyl group attached to the benzene ring.
- The presence of the methyl group in toluene can cause deviations from Raoult's Law due to steric hindrance and differences in intermolecular forces.
- Therefore, the pair of benzene and toluene is likely to form a non-ideal solution.

In summary, the pair of C6H6 and toluene (benzene and toluene) forms a non-ideal solution due to the presence of an additional methyl group in toluene, leading to deviations from Raoult's Law. The other three pairs (CCl4 and SiCl4, C6H5Cl and C6H5Br, CHCl3 and CCl4) are likely to form ideal solutions due to similar molecular structures and intermolecular forces.

3) CHCl3 and CCl4