In which molecule/ion there are more than one type of XO bond lengths
`{:((a)NO_(3)^(-),,,,(b)Cr_(2)O_(7)^(2-)),((c )HCOO^(-),,,,(d)HClO_(3)),((e)PO_(4)^(3-),,,,(f)SO_(4)^(2-)):}`
correct code is

Options

A. a,b,d
B. b,d
C. b,c,d,f
D. a,b,c,f

Answer

To determine which molecule or ion has more than one type of XO bond length, we will analyze each option step by step.

### Step 1: Analyze Option A - NO₃⁻ (Nitrate Ion)
The nitrate ion has the structure:
```
O
||
N -- O⁻
|
O⁻
```
Nitrate exhibits resonance, where the double bond can be between nitrogen and any of the three oxygen atoms. All bond lengths are equivalent due to resonance.

**Conclusion for A:** All bond lengths are the same.

**Hint:** Check for resonance structures to determine if bond lengths are the same.

---

### Step 2: Analyze Option B - Cr₂O₇²⁻ (Dichromate Ion)
The dichromate ion can be represented as:
```
O
||
Cr -- O -- Cr
||
O
|
O⁻
```
In this structure, there are two types of bonds: the double bonds (Cr=O) and the single bond (Cr-O⁻). The single bond has a different bond length compared to the double bond.

**Conclusion for B:** There are different bond lengths.

**Hint:** Look for different types of bonds (single vs double) in the structure.

---

### Step 3: Analyze Option C - HCOO⁻ (Formate Ion)
The formate ion has the structure:
```
O
||
H -- C -- O⁻
```
Similar to the nitrate ion, formate also exhibits resonance, leading to equal bond lengths.

**Conclusion for C:** All bond lengths are the same.

**Hint:** Identify if resonance leads to equivalent bond lengths.

---

### Step 4: Analyze Option D - HClO₃ (Chloric Acid)
The structure of chloric acid is:
```
O
||
Cl -- O
|
OH
```
In this case, the Cl=O bond is a double bond, while the Cl-OH bond is a single bond. Thus, there are different bond lengths.

**Conclusion for D:** There are different bond lengths.

**Hint:** Check if any oxygen atoms are involved in different types of bonds.

---

### Step 5: Analyze Option E - PO₄³⁻ (Phosphate Ion)
The phosphate ion structure is:
```
O
||
P -- O⁻
|
O⁻
|
O⁻
```
Phosphate also exhibits resonance, leading to equal bond lengths among all P-O bonds.

**Conclusion for E:** All bond lengths are the same.

**Hint:** Look for resonance that equalizes bond lengths.

---

### Step 6: Analyze Option F - SO₄²⁻ (Sulfate Ion)
The sulfate ion has the structure:
```
O
||
S -- O⁻
|
O⁻
|
O
```
Similar to the previous cases, sulfate exhibits resonance, resulting in equal bond lengths.

**Conclusion for F:** All bond lengths are the same.

**Hint:** Identify resonance structures to determine bond length uniformity.

---

### Final Conclusion
The molecules/ions with more than one type of XO bond lengths are:
- **Option B: Cr₂O₇²⁻ (Dichromate Ion)**
- **Option D: HClO₃ (Chloric Acid)**

Thus, the correct answer is **B and D**.