Arrange the following compounds in increasing order of reactivity towards the addition of HBr RCH = CHR, `C`H_(2)` =`C`H_(2)`, `R_(2)`C = CHR, `R_(2)` = `C`R_(2)`

Options

A. `CH_(2)=CH_(2) lt RCH =CHR lt R_(2)C=CHR lt R_(2)C=CR_(2)`
B. `R_(2)C=CHR lt RCH=CHR lt CH_(2)=CH_(2)lt R_(2)C=CR_(2)`
C. `RCH=CHR lt R_(2)C=CR_(2) lt R_(2)C=CHR lt CH_(2)=CH_(2)`
D. `R_(2)C=CR_(2) lt CH_(2)=CH_(2) lt RCH=CHR lt R_(2)C=CHR`

Explanation

To determine the increasing order of reactivity of the given compounds towards the addition of HBr, we need to analyze the structure of each compound and the influence of alkyl groups on the reactivity of the double bond.

### Step-by-Step Solution:

1. **Identify the Compounds**:
The compounds given are:
- A: RCH = CHR
- B: CH₂ = CH₂
- C: R₂C = CHR
- D: R₂C = CR₂

2. **Understand the Role of Alkyl Groups**:
Alkyl groups are electron-donating due to their +I (inductive) effect. The more alkyl groups attached to the double-bonded carbon atoms, the higher the electron density on those carbons. This increased electron density enhances the reactivity towards electrophiles like HBr.

3. **Analyze Each Compound**:
- **Compound A (RCH = CHR)**: Contains two alkyl groups (R) attached to the double bond. This will have moderate reactivity.
- **Compound B (CH₂ = CH₂)**: Contains no alkyl groups. This will have the least reactivity.
- **Compound C (R₂C = CHR)**: Contains one carbon with two alkyl groups (R) and one with one alkyl group (R). This will have higher reactivity than A.
- **Compound D (R₂C = CR₂)**: Contains two carbons each with two alkyl groups (R). This will have the highest reactivity.

4. **Rank the Compounds**:
Based on the analysis:
- Least reactive: B (CH₂ = CH₂) - no alkyl groups
- Next: A (RCH = CHR) - two alkyl groups
- Next: C (R₂C = CHR) - one carbon with two alkyl groups
- Most reactive: D (R₂C = CR₂) - both carbons have two alkyl groups

5. **Final Order**:
The increasing order of reactivity towards the addition of HBr is:
**B < A < C < D**