Which of the following statements are correct 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 preparede when `(P//F)` (phenol//formaldehyde) ratio is greater than 1, Whereas bakelite is prepared when `(P//F)` ratio is less than 1.
D. Novolac is prepared when `P//Flt1` , and bakelite is prepared when `P//Fgt1` .

Answer

To determine which statements about phenol-formaldehyde resin are correct, let's analyze the provided options step by step.

### Step 1: Understand the Types of Phenol-Formaldehyde Resins
Phenol-formaldehyde resins can be categorized into two main types based on the phenol to formaldehyde (P/F) ratio:
- **Novolac**: This is a type of phenol-formaldehyde resin where the P/F ratio is greater than 1. It is typically used in the manufacturing of adhesives.
- **Bakelite**: This is a thermosetting phenol-formaldehyde resin formed when the P/F ratio is less than 1. It is known for its electrical non-conductivity and heat-resistant properties.

### Step 2: Analyze Each Statement
1. **Statement 1**: "Novolac is used in the manufacturing of adhesive."
- **Analysis**: This statement is correct. Novolac resins are indeed used to make adhesives.

2. **Statement 2**: "Bakelite is a cross-linked polymer and is used in making switches and plugs."
- **Analysis**: This statement is partially correct. While Bakelite is a cross-linked polymer, it is primarily used for its electrical non-conductivity and heat-resistant properties in applications like electrical insulators, radio, and telephone casings, rather than specifically for making switches and plugs.

3. **Statement 3**: "Novolac is prepared when P/F ratio is greater than 1, while Bakelite is prepared when P/F ratio is less than 1."
- **Analysis**: This statement is correct. Novolac is indeed prepared when the P/F ratio is greater than 1, and Bakelite is prepared when the P/F ratio is less than 1.

4. **Statement 4**: "Novolac is prepared when P/F is greater than 1."
- **Analysis**: This statement is incorrect. It is a repetition of the correct information but does not provide any new insight.

### Conclusion
Based on the analysis:
- **Correct Statements**: 1 and 3
- **Incorrect Statements**: 2 and 4

### Final Answer
The correct statements about phenol-formaldehyde resin are:
1. Novolac is used in the manufacturing of adhesive.
3. Novolac is prepared when the P/F ratio is greater than 1, while Bakelite is prepared when the P/F ratio is less than 1.