Which of the following is linear ?

Options

A. `C_(2)H_(2)`
B. `CH_(4)`
C. `H_(2)O`
D. `NH_(3).`

Explanation

To determine which of the given species is linear, we will analyze the molecular geometry of each compound mentioned in the question.

### Step-by-Step Solution:

1. **Identify the Compounds**: The question involves the following compounds: C2H2 (acetylene), CH4 (methane), H2O (water), and NH3 (ammonia).

2. **Analyze C2H2 (Acetylene)**:
- Structure: Acetylene has a carbon-carbon triple bond and each carbon is bonded to one hydrogen atom.
- Geometry: The bond angle between the hydrogen-carbon-carbon is 180 degrees.
- Conclusion: The shape of C2H2 is linear.

3. **Analyze CH4 (Methane)**:
- Structure: Methane has four hydrogen atoms bonded to a central carbon atom.
- Geometry: The arrangement of these bonds is tetrahedral with bond angles of approximately 109.5 degrees.
- Conclusion: The shape of CH4 is tetrahedral, not linear.

4. **Analyze H2O (Water)**:
- Structure: Water has two hydrogen atoms bonded to a central oxygen atom, with two lone pairs on the oxygen.
- Geometry: The presence of lone pairs causes the molecule to adopt a bent shape with bond angles of about 104.5 degrees.
- Conclusion: The shape of H2O is bent, not linear.

5. **Analyze NH3 (Ammonia)**:
- Structure: Ammonia has three hydrogen atoms bonded to a central nitrogen atom, with one lone pair on the nitrogen.
- Geometry: The shape is trigonal pyramidal due to the lone pair, with bond angles of about 107 degrees.
- Conclusion: The shape of NH3 is pyramidal, not linear.

6. **Final Conclusion**: Among the compounds analyzed, only C2H2 (acetylene) has a linear structure.