Methane, ethane and propane are said to form a homologous series because all are

Options

A. hydrocarbons
B. saturated hydrocarbons
C. aliphatic hydrocarbons
D. differ from each other by `-CH_(2)` group

Explanation

To answer the question, "Methane, ethane, and propane are said to form a homologous series because all are...", we need to understand the characteristics that define a homologous series in organic chemistry.

### Step-by-Step Solution:

1. **Definition of Homologous Series**:
A homologous series is a group of organic compounds that have the same functional group and similar chemical properties, but differ from each other by a specific structural unit.

**Hint**: Remember that a homologous series consists of compounds with similar properties but different structures.

2. **Identifying the Compounds**:
- **Methane (CH₄)**: The simplest alkane with one carbon atom.
- **Ethane (C₂H₆)**: The second member of the alkane series, with two carbon atoms.
- **Propane (C₃H₈)**: The third member of the alkane series, with three carbon atoms.

**Hint**: Identify the number of carbon atoms in each compound to understand their sequence in the series.

3. **Difference in Molecular Formula**:
Each successive member of the series differs by a CH₂ unit:
- From methane (CH₄) to ethane (C₂H₆), the difference is CH₂.
- From ethane (C₂H₆) to propane (C₃H₈), the difference is also CH₂.

**Hint**: Look for the pattern in the molecular formulas to see how each compound is related.

4. **General Formula for Alkanes**:
The general formula for alkanes is CₙH₂ₙ₊₂, where n is the number of carbon atoms. For methane, ethane, and propane, the values of n are 1, 2, and 3 respectively.

**Hint**: Familiarize yourself with the general formula for alkanes to see how it applies to the given compounds.

5. **Saturated Hydrocarbons**:
Methane, ethane, and propane are saturated hydrocarbons, meaning they contain only single bonds between carbon atoms.

**Hint**: Remember that saturation refers to the presence of only single bonds in the compounds.

6. **Conclusion**:
Therefore, methane, ethane, and propane form a homologous series because they:
- Have the same functional group (alkanes).
- Differ by a CH₂ unit.
- Follow the same general formula (CₙH₂ₙ₊₂).
- Are saturated hydrocarbons.

**Final Answer**: Methane, ethane, and propane are said to form a homologous series because all are saturated hydrocarbons that differ from each other by a CH₂ unit.