Which pair of molecules are polar species ?

Options

A. `CO_(2) and H_(2)O`
B. `BF_(3) and PCl_(3)`
C. `SO_(2) and SCl_(2)`
D. `CS_(2) and SO_(3)`

Explanation

To determine which pair of molecules are polar species, we need to analyze the given options based on the concept of polarity and dipole moments. A molecule is considered polar if it has a net dipole moment that is not equal to zero, meaning that the distribution of electron density is uneven.

### Step-by-Step Solution:

1. **Understand Polarity**:
- A polar molecule has a dipole moment that is not equal to zero. This occurs when there is an uneven distribution of electron density, usually due to differences in electronegativity between bonded atoms.

2. **Analyze the Given Options**:
- The options are:
- A) CO2 and H2O
- B) BF3 and PCl3
- C) SO2 and SCl2
- D) CS2 and SO3

3. **Examine Each Pair**:
- **A) CO2 and H2O**:
- CO2 is linear and symmetrical, resulting in a net dipole moment of zero (non-polar).
- H2O is bent and has a net dipole moment due to the difference in electronegativity between H and O (polar).
- **B) BF3 and PCl3**:
- BF3 is symmetrical and non-polar (dipole moment = 0).
- PCl3 is trigonal pyramidal and has a net dipole moment (polar).
- **C) SO2 and SCl2**:
- SO2 is bent and has a net dipole moment (polar).
- SCl2 is also bent and has a net dipole moment (polar).
- **D) CS2 and SO3**:
- CS2 is linear and symmetrical (non-polar).
- SO3 is symmetrical (non-polar).

4. **Identify Polar Pairs**:
- From the analysis:
- A) CO2 (non-polar) and H2O (polar) - Not a pair of polar molecules.
- B) BF3 (non-polar) and PCl3 (polar) - Not a pair of polar molecules.
- C) SO2 (polar) and SCl2 (polar) - Both are polar molecules.
- D) CS2 (non-polar) and SO3 (non-polar) - Not a pair of polar molecules.

5. **Conclusion**:
- The pair of molecules that are both polar species is **C) SO2 and SCl2**.

### Final Answer:
The pair of molecules that are polar species is **C) SO2 and SCl2**.