(A): `NO_(3)^(-)` and `CO_(3)^(-2)` ions are isoelectronic.
(R): Nitrate ion is planar 

Options

A. Both A & R are true, R is the correct explanation of A
B. Both A & R are true, R is not correct explanation of A
C. A is true, R is false
D. A is false, R is true

Answer

To solve the question regarding the assertion (A) and reason (R) about the nitrate ion (NO₃⁻) and carbonate ion (CO₃²⁻), we will follow these steps:

### Step 1: Determine the number of electrons in NO₃⁻
- The nitrate ion (NO₃⁻) consists of:
- 1 nitrogen atom (N), which has 7 electrons.
- 3 oxygen atoms (O), each contributing 8 electrons, so 3 × 8 = 24 electrons.
- Since it has a negative charge (-1), we add 1 more electron.

**Calculation:**
\[ \text{Total electrons in NO}_3^- = 7 + 24 + 1 = 32 \text{ electrons} \]

### Step 2: Determine the number of electrons in CO₃²⁻
- The carbonate ion (CO₃²⁻) consists of:
- 1 carbon atom (C), which has 6 electrons.
- 3 oxygen atoms (O), each contributing 8 electrons, so 3 × 8 = 24 electrons.
- Since it has a -2 charge, we add 2 more electrons.

**Calculation:**
\[ \text{Total electrons in CO}_3^{2-} = 6 + 24 + 2 = 32 \text{ electrons} \]

### Step 3: Compare the electron counts
- Both NO₃⁻ and CO₃²⁻ have a total of 32 electrons, confirming that they are isoelectronic.

### Step 4: Analyze the structure of NO₃⁻
- The structure of the nitrate ion is:
- It has one nitrogen atom bonded to three oxygen atoms, with one double bond and two single bonds.
- The nitrogen atom undergoes sp² hybridization, which results in a planar structure.

### Step 5: Conclusion
- Assertion (A) is true: NO₃⁻ and CO₃²⁻ are isoelectronic.
- Reason (R) is also true: The nitrate ion is planar.
- However, the reason (R) does not explain the assertion (A) because the isoelectronic nature does not depend on the planarity of the nitrate ion.

### Final Answer
- Both A and R are true, but R is not the correct explanation of A. Thus, the answer is option 2.

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