Which of the following statements is incorrect for a homologous series ?

Options

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

Answer

To determine which statement is incorrect regarding a homologous series, we need to understand the characteristics of such series in organic chemistry. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the 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 by a constant unit, typically a -CH2- group.

**Hint:** Remember that the key feature of a homologous series is the presence of a common functional group and a consistent difference in molecular formula.

### Step 2: Identify the General Formula
For alkanes, the general formula is CnH2n+2. For alkenes, it is CnH2n, and for alkynes, it is CnH2n-2. This means that all members of a homologous series will conform to a specific general formula.

**Hint:** Look for the pattern in the molecular formulas of the compounds in the series.

### Step 3: Analyze the Chemical Properties
Members of a homologous series have similar chemical properties due to the presence of the same functional group. For example, all alcohols will react similarly because they all contain the hydroxyl (-OH) group.

**Hint:** Focus on how the functional group influences the chemical behavior of the compounds.

### Step 4: Examine Physical Properties
Physical properties such as boiling point, melting point, and solubility can vary significantly among members of a homologous series. As the molecular mass increases, these properties can change, leading to differences in state (gas, liquid, solid) at room temperature.

**Hint:** Consider how molecular weight affects physical properties and why they may not be the same across the series.

### Step 5: Review the Statements
Now, let’s review the statements provided:
1. All members have a general formula.
2. All members have the same functional group.
3. All members have the same chemical properties.
4. All members have the same physical properties.

From our analysis:
- Statements 1, 2, and 3 are correct.
- Statement 4 is incorrect because physical properties do vary among members of a homologous series.

### Conclusion
The incorrect statement regarding a homologous series is that all members have the same physical properties.

**Final Answer:** All members have the same physical properties (This statement is incorrect).