in which of the following reaction sayzeff alkene is major product ?

Options

A. `CH_(3)-CH_(2)- underset(Br)underset(|)overset(CH_(3))overset(|) C-Choverset(o+)Nme_(3) underset(Delta)overset(HO^(-))`
B. `CH_(3)-CH_(2)-CH_(2)-underset(f)underset(|)CH -CH-CH_(3)underset(Delta)oversert(ETO^(-))to`
C. `CH_(3)-CH_(2)- underse(Br)underset(|)overset(CH_(3))overset(|)C-CH_(3) underset(Delta)overset(t-BuOK)to`
D. `CH_(3)-CH_(2)-CH_(2)-underset(CH_(3))underset(|)overset(Br)overset(|)C -CH_(3) underset(Delta)overset(CH_(3)OK)to`

Explanation

To determine in which reaction the Saytzeff alkene is the major product, we need to analyze each reaction option provided. The Saytzeff rule states that the more substituted alkene will be the major product in elimination reactions.

### Step-by-Step Solution:

1. **Understand Saytzeff and Hoffman Products**:
- Saytzeff (or Zaitsev) alkene: The more substituted alkene (more alkyl groups attached to the double bond).
- Hoffman alkene: The less substituted alkene (fewer alkyl groups attached to the double bond).

2. **Analyze Reaction A**:
- The leaving group is NMe3, which is a weak leaving group.
- The elimination reaction will lead to the formation of a carbocation.
- The most stable carbocation formed will dictate the product. However, due to the weak leaving group, the major product formed will be the Hoffman product.
- **Conclusion for A**: Major product is Hoffman alkene.

3. **Analyze Reaction B**:
- The leaving group is fluoride (F), which is also a weak leaving group.
- Similar to reaction A, the elimination will lead to the formation of a carbocation.
- The product formed will again be the Hoffman alkene due to the weak leaving group.
- **Conclusion for B**: Major product is Hoffman alkene.

4. **Analyze Reaction C**:
- The leaving group is bromine (Br), which is a good leaving group.
- A stable tertiary carbocation will form, allowing for the elimination to yield the more substituted alkene.
- Since Br is a good leaving group, the Saytzeff product will be favored here.
- **Conclusion for C**: Major product is Saytzeff alkene.

5. **Analyze Reaction D**:
- The leaving group is also bromine (Br), and the nucleophile is a small base (CH3O-).
- The base can easily abstract a proton from a more substituted carbon, leading to the formation of the Saytzeff product.
- **Conclusion for D**: Major product is Saytzeff alkene.

### Final Answer:
The reaction in which the Saytzeff alkene is the major product is **C and D**.