Which of the following chemical species is linear, planar as well as polar?

Options

A. HCN
B. `XeF_2`
C. `I_3^(-)`
D. `XeF_4`

Answer

To solve the question of which chemical species is linear, planar, and polar, we will analyze each option step by step.

### Step 1: Analyze SCN⁻ (Thiocyanate Ion)
- **Structure**: The structure of SCN⁻ involves a sulfur atom (S) bonded to a carbon atom (C), which is triple-bonded to a nitrogen atom (N). This gives us a linear arrangement.
- **Hybridization**: The hybridization of the carbon atom is sp, which confirms the linear geometry.
- **Polarity**: The dipole moment does not cancel out because of the difference in electronegativity between S and N. Thus, SCN⁻ is polar.

**Conclusion**: SCN⁻ is linear, planar, and polar.

### Step 2: Analyze XCF₂ (Hypothetical Compound)
- **Structure**: XCF₂ has a central atom X bonded to two fluorine atoms (F) and has three lone pairs of electrons.
- **Geometry**: The presence of three lone pairs results in a linear geometry due to the arrangement of the bonding pairs and lone pairs.
- **Polarity**: The dipole moments of the two C-F bonds cancel out due to symmetry, leading to a non-polar molecule.

**Conclusion**: XCF₂ is linear but non-polar and not planar.

### Step 3: Analyze I₃⁻ (Iodide Ion)
- **Structure**: I₃⁻ consists of three iodine atoms arranged linearly.
- **Geometry**: The hybridization is sp, which confirms a linear structure.
- **Polarity**: The dipole moments do not cancel out completely due to the presence of the negative charge, making it polar.

**Conclusion**: I₃⁻ is linear and polar but not planar.

### Step 4: Analyze XCF₄ (Hypothetical Compound)
- **Structure**: XCF₄ has a central atom X bonded to four fluorine atoms and has two lone pairs.
- **Geometry**: The presence of lone pairs leads to a square planar arrangement.
- **Polarity**: The dipole moments of the C-F bonds cancel out due to symmetry, resulting in a non-polar molecule.

**Conclusion**: XCF₄ is planar but non-linear and non-polar.

### Final Conclusion
After analyzing all options, the only species that is linear, planar, and polar is **SCN⁻**.