Which of the following pair of species are iso-electronic ?

Options

A. `CN^(-)&NO^(+)`
B. `N_(2)^(-)&N_(2)^(+)`
C. `H_(2)^(o+)&H_(2)^(-)`
D. `CO&NO^(-)`

Answer

To determine which pairs of species are isoelectronic, we need to find out how many electrons each species has. Isoelectronic species have the same number of electrons. Let's analyze the pairs step by step.

### Step 1: Analyze CN⁻
- CN⁻ (Cyanide ion) consists of carbon (C) and nitrogen (N).
- Carbon has 6 electrons, and nitrogen has 7 electrons.
- CN has a total of 6 + 7 = 13 electrons.
- The negative charge (−1) adds one more electron, making a total of 14 electrons.

### Step 2: Analyze NO⁺
- NO⁺ (Nitric oxide ion) consists of nitrogen (N) and oxygen (O).
- Nitrogen has 7 electrons, and oxygen has 8 electrons.
- NO has a total of 7 + 8 = 15 electrons.
- The positive charge (+1) removes one electron, making a total of 14 electrons.

### Step 3: Analyze N₂⁻
- N₂⁻ (Nitrogen molecule with a negative charge) consists of two nitrogen atoms.
- Each nitrogen has 7 electrons, so N₂ has a total of 7 + 7 = 14 electrons.
- The negative charge (−1) adds one more electron, making a total of 15 electrons.

### Step 4: Analyze N₂⁺
- N₂⁺ (Nitrogen molecule with a positive charge) consists of two nitrogen atoms.
- Each nitrogen has 7 electrons, so N₂ has a total of 14 electrons.
- The positive charge (+1) removes one electron, making a total of 13 electrons.

### Step 5: Analyze H₂⁺
- H₂⁺ (Dihydrogen ion) consists of two hydrogen atoms.
- Each hydrogen has 1 electron, so H₂ has a total of 1 + 1 = 2 electrons.
- The positive charge (+1) removes one electron, making a total of 1 electron.

### Step 6: Analyze H₂⁻
- H₂⁻ (Dihydrogen ion with a negative charge) consists of two hydrogen atoms.
- Each hydrogen has 1 electron, so H₂ has a total of 2 electrons.
- The negative charge (−1) adds one more electron, making a total of 3 electrons.

### Step 7: Analyze CO
- CO (Carbon monoxide) consists of carbon (C) and oxygen (O).
- Carbon has 6 electrons, and oxygen has 8 electrons.
- CO has a total of 6 + 8 = 14 electrons.

### Step 8: Analyze NO⁻
- NO⁻ (Nitric oxide ion with a negative charge) consists of nitrogen (N) and oxygen (O).
- Nitrogen has 7 electrons, and oxygen has 8 electrons.
- NO has a total of 7 + 8 = 15 electrons.
- The negative charge (−1) adds one more electron, making a total of 16 electrons.

### Conclusion
Now we summarize the total number of electrons for each species:
- CN⁻: 14 electrons
- NO⁺: 14 electrons
- N₂⁻: 15 electrons
- N₂⁺: 13 electrons
- H₂⁺: 1 electron
- H₂⁻: 3 electrons
- CO: 14 electrons
- NO⁻: 16 electrons

From the analysis, the pairs that are isoelectronic (same number of electrons) are:
- CN⁻ and NO⁺ (both have 14 electrons)
- CN⁻ and CO (both have 14 electrons)

### Final Answer
The pairs of species that are isoelectronic are CN⁻ and NO⁺, and CN⁻ and CO.