Isoelectronic species have the same number of electrons. This property is not only restricted to atoms but also observed in molecules and ions.
Which of the following sets of isoelectronic species does not have the same shape? 

Options

A. `H_2S `and `HCI`
B. `NO_3^(-)` and `CO_(3)^(2-)`
C. `CIO_(4)^(-)` and `SO_(4)^(2-)`
D. `NO_(2)^(+)` and `CO_2`

Answer

To determine which set of isoelectronic species does not have the same shape, we need to analyze the molecular geometry of each species in the provided options. Here’s a step-by-step solution:

### Step 1: Identify the Isoelectronic Species
First, we need to identify the isoelectronic species in the options provided. Isoelectronic species have the same number of electrons.

### Step 2: Determine the Valence Electrons
Next, we will calculate the total number of valence electrons for each species:
- For **SO2^2-** (sulfite ion): Sulfur has 6 valence electrons, and each oxygen has 6. Therefore, for SO2^2-, we have:
- Sulfur: 6
- Oxygen (2): 6 x 2 = 12
- Charge: +2 (adds 2 electrons)
- Total = 6 + 12 + 2 = 20 electrons

- For **NO2^+** (nitronium ion): Nitrogen has 5 valence electrons, and each oxygen has 6. Therefore, for NO2^+, we have:
- Nitrogen: 5
- Oxygen (2): 6 x 2 = 12
- Charge: -1 (removes 1 electron)
- Total = 5 + 12 - 1 = 16 electrons

- For **CO2** (carbon dioxide): Carbon has 4 valence electrons, and each oxygen has 6. Therefore, for CO2, we have:
- Carbon: 4
- Oxygen (2): 6 x 2 = 12
- Total = 4 + 12 = 16 electrons

### Step 3: Analyze the Molecular Geometry
Now, we will analyze the molecular geometry of each of the isoelectronic species:
- **SO2^2-**: This species has a bent shape due to the presence of lone pairs on the sulfur atom.
- **NO2^+**: This species has a linear shape because it has no lone pairs on the nitrogen atom and has two oxygen atoms bonded to it.
- **CO2**: This species also has a linear shape due to the double bonds between carbon and oxygen.

### Step 4: Compare the Shapes
Now we can compare the shapes of the isoelectronic species:
- **SO2^2-** has a bent shape.
- **NO2^+** has a linear shape.
- **CO2** also has a linear shape.

### Conclusion
From the analysis, we can conclude that the set of isoelectronic species that do not have the same shape is **SO2^2-** (bent) and **NO2^+** and **CO2** (both linear). Therefore, the answer is **SO2^2-**.