Which of the following statements are incorrect about phenol formaldehyde resin ?

Options

A. Novolac or resol is a linear polymer and is used in the manufacture of adhesive
B. Bakelite is a cross linked polymer and is used in making switches and plugs
C. Novolac is prepared when (P/F) (phenol/formaldehyde) ratio if greater than 1, whereas bakelite is prepared when (P/F) ratio is less than 1
D. Novolac is prepared when `P//F lt 1` , and bakelite is prepared when `P//F gt 1`

Answer

To determine which statement is incorrect about phenol formaldehyde resin, we need to analyze each option based on our understanding of Novolac and Bakelite, the two types of phenol formaldehyde resins.

### Step-by-Step Solution:

1. **Understanding Novolac and Bakelite**:
- Novolac and Bakelite are both derived from the reaction of phenol and formaldehyde.
- Novolac is a linear polymer, while Bakelite is a cross-linked polymer.

2. **Analyzing the Options**:
- **Option 1**: "Novolac or Rezol is a linear polymer and used in the manufacture or as adhesive."
- This statement is **true**. Novolac is indeed a linear polymer and is used as an adhesive.

- **Option 2**: "Bakelite is a cross-linked polymer and used in making switches and plugs."
- This statement is **true**. Bakelite is a cross-linked polymer and is commonly used in electrical applications like switches and plugs.

- **Option 3**: "Novolac is prepared when P by F ratio (phenol to formaldehyde ratio) is greater than 1 whereas Bakelite is prepared when P by F ratio is less than 1."
- This statement is **true**. Novolac is formed when there is more phenol than formaldehyde (P/F > 1), and Bakelite is formed when there is more formaldehyde than phenol (P/F < 1).

- **Option 4**: "Novolac is prepared when P by F ratio is less than 1 and Bakelite is prepared when P by F ratio is greater than 1."
- This statement is **false**. This is the incorrect statement because Novolac is prepared when P/F ratio is greater than 1, not less than 1.

3. **Conclusion**:
- The incorrect statement about phenol formaldehyde resin is **Option 4**.

### Final Answer:
The incorrect statement about phenol formaldehyde resin is **Option 4**.

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