Which of the following statement is true?

Options

A. In `[PtCl_(2)(NH_(3))_(2)]^(2+)` the cis form is optically inactive while trans form is optically active
B. In `[Fe(C_(2)O_(4))_(3)]^(3-)`, geometrical isomerism does not exist while optical isomerism exists
C. In Mabcd, square planar complexes show both optical as well as geometrical isomerism
D. In Mabcd tetrahedral compoex, optical isomerism cannot be observed

Explanation

To determine which statement is true regarding coordination compounds, we will analyze each statement step by step.

### Step 1: Analyze the first statement
The first statement claims that the complex \( \text{PtCl}_2\text{NH}_3 \) (cis form) is optically inactive while the trans form is optically active.

- **Cis form**: In the cis form, the two chloride ligands are adjacent to each other, which leads to a symmetrical arrangement. This symmetry means that the molecule can be superimposed on its mirror image, making it optically inactive.
- **Trans form**: In the trans form, the two chloride ligands are opposite each other. However, this arrangement also leads to a symmetrical structure, which means that it too can be superimposed on its mirror image, rendering it optically inactive.

**Conclusion**: Both forms are optically inactive. Therefore, this statement is **false**.

### Step 2: Analyze the second statement
The second statement claims that in oxalate complexes, geometrical isomerism does not exist while optical isomerism does exist.

- **Geometrical isomerism**: Oxalate is a bidentate ligand, which means it can attach to the metal at two points. In octahedral complexes with oxalate, geometrical isomers can exist (cis and trans forms). Thus, geometrical isomerism does exist.
- **Optical isomerism**: Because oxalate can create non-superimposable mirror images when coordinated to a metal, optical isomerism can occur.

**Conclusion**: This statement is **false** because geometrical isomerism does exist.

### Step 3: Analyze the third statement
The third statement claims that in \( \text{MA} \text{BCD} \) square planar complexes, both optical and geometrical isomerism can occur.

- **Square planar complexes**: In square planar complexes, if there are two identical ligands, geometrical isomerism cannot occur because the arrangement would lead to symmetry. Therefore, geometrical isomerism is not possible if there are two identical ligands.
- **Optical isomerism**: Optical isomerism can occur if the arrangement of ligands creates a chiral center.

**Conclusion**: This statement is **false** because geometrical isomerism cannot occur with two identical ligands.

### Step 4: Analyze the fourth statement
The fourth statement claims that in \( \text{MABCD} \) tetrahedral complexes, optical isomerism cannot be observed.

- **Tetrahedral complexes**: Tetrahedral complexes can exhibit optical isomerism if all four ligands are different. If there are two or more identical ligands, then the complex may not be chiral, and thus optical isomerism cannot be observed.

**Conclusion**: This statement is **false** because optical isomerism can be observed in tetrahedral complexes with all different ligands.

### Final Conclusion
After analyzing all statements, the only true statement is regarding the oxalate complexes where geometrical isomerism does exist, which contradicts the second statement. Therefore, the correct answer is:

**The true statement is: None of the options provided are true.**