Complex compounds that have the same molecular formula but have different structural/space arrangements of ligands around central metal atom/ion are called isomers, these are of two types namely structural and stereoisomers.
Q. Complex species that exhibits isomerism is:

Options

A. `[Ag(NH_(3))_(2)]^(+)`
B. `[Co(NO_(2))(NH_(3))_(5)]^(2+)`
C. `[PtCl_(2)(en)]`
D. `[CoCl(NH_3)_(5)]^(2-)`

Answer

To solve the question regarding complex species that exhibit isomerism, we will analyze the provided options step by step.

### Step 1: Understand the Concept of Isomerism
Isomerism in coordination compounds refers to the phenomenon where compounds have the same molecular formula but different arrangements of ligands around the central metal atom/ion. There are two main types of isomerism: structural isomerism and stereoisomerism.

**Hint:** Remember that isomers have the same molecular formula but differ in structure or spatial arrangement.

### Step 2: Identify Types of Isomerism
- **Structural Isomerism:** Different connectivity of ligands.
- **Stereoisomerism:** Same connectivity but different spatial arrangements, which includes:
- **Geometrical Isomerism:** Different arrangements of ligands in space (cis/trans).
- **Optical Isomerism:** Non-superimposable mirror images.

**Hint:** Distinguish between the types of isomerism to identify which complexes may exhibit them.

### Step 3: Analyze Each Option
1. **Ag(NH3)2:**
- This complex has a linear structure and does not exhibit isomerism due to its symmetry.
- **Conclusion:** Incorrect.

2. **Co(NO2)2(NH3)4:**
- In this complex, if both NO2 ligands are adjacent, it is a cis isomer. If they are opposite, it is a trans isomer.
- Both arrangements do not show optical isomerism due to symmetry but do show geometrical isomerism.
- **Conclusion:** Correct.

3. **[CoCl2(en)2]:**
- Ethylene diamine (en) is a bidentate ligand. The arrangement can lead to cis/trans forms, but without a trans isomer, we cannot classify it as cis.
- **Conclusion:** Incorrect.

4. **[CoCl(NH3)5]:**
- With only one chlorine ligand and five ammonia ligands, there is no possibility of isomerism due to lack of different arrangements.
- **Conclusion:** Incorrect.

### Step 4: Final Conclusion
Based on the analysis, the complex that exhibits isomerism is **Co(NO2)2(NH3)4**, which can exist in both cis and trans forms, demonstrating geometrical isomerism.

**Final Answer:** The complex species that exhibits isomerism is **Co(NO2)2(NH3)4**.

---