Which one is not correct for a homologous series?

Options

A. All members have one general formula
B. All members have same chemical properties
C. All members have same physical properties
D. All members have same functional group

Answer

To determine which statement is not correct for a homologous series, we need to understand the characteristics of a homologous series in organic chemistry. Here’s a step-by-step solution:

### Step 1: Define Homologous Series
A homologous series is a group of organic compounds that have the same functional group and similar chemical properties, but differ by a constant unit (usually -CH2) in their molecular formula.

### Step 2: Identify General Formula
Each member of a homologous series can be represented by a general formula. For example:
- Alkanes: CnH2n+2
- Alkenes: CnH2n
- Alkynes: CnH2n-2

### Step 3: Analyze the Statements
Now let's analyze the statements provided in the question:
1. All members have the same general formula.
2. All members have the same chemical properties.
3. All members have the same physical properties.
4. All members have the same functional group.

### Step 4: Evaluate Each Statement
1. **Same General Formula**: This is correct. All members of a homologous series share a general formula.
2. **Same Chemical Properties**: This is also correct. Members of the same series react similarly due to having the same functional group.
3. **Same Physical Properties**: This is **not correct**. Physical properties (like boiling point, melting point, etc.) can vary significantly among members of a homologous series, especially as the size of the molecule increases.
4. **Same Functional Group**: This is correct. All members of a homologous series have the same functional group.

### Step 5: Conclusion
Based on the evaluation, the statement that is not correct for a homologous series is: **"All members have the same physical properties."**

### Final Answer
The answer is option 3.

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