Which of the following statement (s) is /are correct?
(I) In acidic solution dichromate ions are converted to chromate ions .
(II) An acidified solution of `K_(2)Cr_(2)O_(7)` liberates iodine from iodides.
(III) Potassium dichromate is used as a titrant for `Fe^(2+)` ions.
(IV) Ammonium dichromate on heating undergo exothermic decomposition to give `Cr_(2)O_(3)`.
Choose the correct option .

Options

A. I,II and III
B. II,III, and IV
C. I,II,III and IV
D. II and III

Explanation

To determine which of the statements are correct, let's analyze each statement one by one.

### Step 1: Analyze Statement I
**Statement I**: In acidic solution, dichromate ions are converted to chromate ions.

- **Analysis**: This statement is incorrect. In acidic solutions, dichromate ions \((Cr_2O_7^{2-})\) are not converted to chromate ions \((CrO_4^{2-})\). Instead, they remain as dichromate ions. The conversion from dichromate to chromate occurs in alkaline solutions.

### Step 2: Analyze Statement II
**Statement II**: An acidified solution of \(K_2Cr_2O_7\) liberates iodine from iodides.

- **Analysis**: This statement is correct. In an acidified solution, potassium dichromate (\(K_2Cr_2O_7\)) can oxidize iodide ions \((I^-)\) to iodine \((I_2)\). The reaction can be represented as:
\[ K_2Cr_2O_7 + 14H^+ + 6I^- \rightarrow 2Cr^{3+} + 7H_2O + 3I_2 \]
Thus, iodine is liberated from iodides.

### Step 3: Analyze Statement III
**Statement III**: Potassium dichromate is used as a titrant for \(Fe^{2+}\) ions.

- **Analysis**: This statement is correct. Potassium dichromate is commonly used as a titrant in redox titrations involving \(Fe^{2+}\) ions. The half-reaction for the dichromate reduction and the oxidation of \(Fe^{2+}\) to \(Fe^{3+}\) confirms this:
\[ Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O \]
\[ Fe^{2+} \rightarrow Fe^{3+} + e^- \]
By balancing these reactions, we can see that potassium dichromate effectively titrates \(Fe^{2+}\).

### Step 4: Analyze Statement IV
**Statement IV**: Ammonium dichromate on heating undergoes exothermic decomposition to give \(Cr_2O_3\).

- **Analysis**: This statement is correct. Ammonium dichromate \((NH_4)_2Cr_2O_7\) decomposes upon heating to produce chromium(III) oxide \((Cr_2O_3)\), nitrogen gas \((N_2)\), and water. The reaction is exothermic and can be represented as:
\[ (NH_4)_2Cr_2O_7 \rightarrow Cr_2O_3 + N_2 + 4H_2O \]
The reaction is characterized by the release of heat and an orange spark.

### Conclusion
Based on the analysis:
- **Statement I**: Incorrect
- **Statement II**: Correct
- **Statement III**: Correct
- **Statement IV**: Correct

Thus, the correct statements are II, III, and IV.

### Final Answer
The correct option is **II, III, and IV**.

---