The decreasing order of reactivity of the following alkenes is:
i. `2, 3` -Dimethyl-`2` butene
ii. `2`- Methyl-`2` butene
`2`- Butene
iv. Ethene

Options

A. `(iv) gt (iii) gt (ii) gt (i)`
B. `(i) gt (ii) gt (iii) gt (iv)`
C. `(iv) gt (ii) gt (iii) gt (i)`
D. `(i) gt (iii) gt (ii) gt (iv)`

Explanation

To determine the decreasing order of reactivity of the given alkenes, we need to analyze their stability based on the number of alpha hydrogens. The stability of alkenes is inversely proportional to their reactivity, meaning that the more stable an alkene is, the less reactive it will be.

### Step-by-Step Solution:

1. **Identify the Alkenes**: The alkenes given are:
- i. 2,3-Dimethyl-2-butene
- ii. 2-Methyl-2-butene
- iii. 2-Butene
- iv. Ethene

2. **Draw the Structures**:
- **2,3-Dimethyl-2-butene**:
- Structure: CH3C(CH3)=C(CH3)CH3
- Number of alpha hydrogens: 12 (6 from each sp3 carbon)
- **2-Methyl-2-butene**:
- Structure: CH3C(CH3)=C(CH3)CH3
- Number of alpha hydrogens: 9 (3 from each sp3 carbon)
- **2-Butene**:
- Structure: CH3CH=CHCH3
- Number of alpha hydrogens: 6 (3 from each sp3 carbon)
- **Ethene**:
- Structure: CH2=CH2
- Number of alpha hydrogens: 0 (no sp3 carbons)

3. **Count the Alpha Hydrogens**:
- 2,3-Dimethyl-2-butene: 12 alpha hydrogens
- 2-Methyl-2-butene: 9 alpha hydrogens
- 2-Butene: 6 alpha hydrogens
- Ethene: 0 alpha hydrogens

4. **Determine Stability**:
- More alpha hydrogens indicate greater stability.
- Stability order (based on alpha hydrogens):
- 2,3-Dimethyl-2-butene (12 alpha H) > 2-Methyl-2-butene (9 alpha H) > 2-Butene (6 alpha H) > Ethene (0 alpha H)

5. **Determine Reactivity**:
- Since reactivity is inversely proportional to stability:
- Ethene (most reactive) > 2-Butene > 2-Methyl-2-butene > 2,3-Dimethyl-2-butene (least reactive)

6. **Write the Decreasing Order of Reactivity**:
- The decreasing order of reactivity is:
- Ethene > 2-Butene > 2-Methyl-2-butene > 2,3-Dimethyl-2-butene

### Final Answer:
The decreasing order of reactivity of the given alkenes is:
**iv. Ethene > iii. 2-Butene > ii. 2-Methyl-2-butene > i. 2,3-Dimethyl-2-butene**