Which of the following is gem halide ?

Options

A. `CH_3CHBrCHBrCH_3`
B. `CH_2Br. CH_2 Br`
C. `CHBr = CHBr`
D. `CH_3CHBr_2`

Explanation

To determine which of the given options is a gem halide, we need to understand the definition of a gem halide. A gem halide (geminal halide) is a compound that has two halogen atoms attached to the same carbon atom.

Let's analyze the options step by step:

1. **Option A: CH3-CH(Br)-CH(Br)-CH3**
- Structure:
```
CH3
|
CH(Br)
|
CH(Br)
|
CH3
```
- In this structure, the two bromine (Br) atoms are attached to different carbon atoms. Therefore, this is **not** a gem halide.

2. **Option B: CH2(Br)-CH2(Br)**
- Structure:
```
CH2(Br)
|
CH2(Br)
```
- Here, both bromine atoms are attached to different carbon atoms as well. Thus, this is also **not** a gem halide.

3. **Option C: CH(Br)=CH(Br)**
- Structure:
```
CH(Br)
||
CH(Br)
```
- In this case, both bromine atoms are again on different carbon atoms. Hence, this is **not** a gem halide.

4. **Option D: CH3-CH(Br)2**
- Structure:
```
CH3
|
CH(Br)
|
Br
```
- Here, both bromine atoms are attached to the same carbon atom (the carbon with the Br groups). Therefore, this is a gem halide.

After analyzing all the options, we conclude that **Option D (CH3-CH(Br)2)** is the gem halide.

### Summary of the Steps:
1. Understand the definition of gem halide.
2. Analyze each option by drawing their structures.
3. Identify the position of halogen atoms in each structure.
4. Conclude which option has both halogens on the same carbon.