The unique behaviour of CU, having a positive `E^(@)` (reduction potential) accounts for its inability to liberate `H_(2)` from acids,. Only oxidising acids (nitric acid and hot concentrated sulphuric acid) react with Cu. The high energy of transform Cu(s) to `Cu^(2+)(aq.)` is not balanced by its hydration enthalpy.
On the other hand, All Cu(II) halides are known except iodide. in this case, `Cu^(2+)` oxidises `I^(-)` to `I_(2)`:
`2Cu^(2+)+4I^(-) to 2CuI(s)+I_(2)`
However, copper (I) compounds are unstable in aqueous solution annd undergo disproportionation.
`2Cu^(+)(aq.)toCu^(2+)(aq.)+Cu`
The stability of `Cu^(2+)(aq.)` rather than `Cu^(+)(aq)` is due to the much more negative `Delta_(Hyd)` of `Cu^(2+)(aq.)` than `Cu^(+)(aq.)`
Q. Select the correct chemical change:

Options

A. `Cu+Dil.H_(2)SO_(4) to CuSO_(4)+H_(2)(g)`
B. `Cu+dil.HNO_(3) to Cu(NO_(3))_(2)+N_(2)O(g)`
C. `CuSO_(4)(aq.)+KCN(excess)toK_(2)[Cu(CN)_(4)]`
D. `CuSO_(4)(aq.)+NH_(4)OH to Cu(OH)_(2)darr`

Explanation

To solve the question regarding the unique behavior of copper (Cu) and its reactions, we will analyze the provided information step by step.

### Step-by-Step Solution:

1. **Understanding Copper's Behavior**:
- Copper has a positive standard reduction potential, which means it does not readily release hydrogen gas from acids. This is because it cannot reduce hydrogen ions to hydrogen gas in non-oxidizing conditions.

**Hint**: Recall that a positive reduction potential indicates a tendency to gain electrons rather than lose them.

2. **Reactions with Oxidizing Acids**:
- Only strong oxidizing acids like concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) can react with copper. This is due to their ability to oxidize copper to Cu²⁺.

**Hint**: Identify which acids are classified as oxidizing acids and their role in oxidizing metals.

3. **Formation of Copper Halides**:
- All copper (II) halides are known except for copper (II) iodide (CuI2). In the presence of iodide ions (I⁻), Cu²⁺ can oxidize I⁻ to form iodine (I2).

**Hint**: Consider the oxidation states of copper and iodine in the reaction.

4. **Disproportionation of Copper (I)**:
- Copper (I) compounds are unstable in aqueous solutions and can undergo disproportionation, where 2 Cu⁺ ions convert to Cu²⁺ and elemental copper (Cu).

**Hint**: Disproportionation involves a single species being oxidized and reduced simultaneously.

5. **Stability of Copper Ions**:
- The stability of Cu²⁺ over Cu⁺ is attributed to the more negative hydration enthalpy (ΔH_hyd) of Cu²⁺ compared to Cu⁺. This means that Cu²⁺ is more stable in solution due to its favorable interaction with water molecules.

**Hint**: Compare the hydration enthalpies of different oxidation states to understand their stability.

6. **Selecting the Correct Chemical Change**:
- Given the reactions mentioned in the video, we need to evaluate the options:
- The first option involves dilute H2SO4, which is incorrect as copper does not react with it.
- The second option involves copper sulfate reacting with NH4OH to form copper hydroxide, which is correct.
- The third option involves copper sulfate reacting with KCN, which is also correct but does not represent the unique behavior of Cu.
- The fourth option is the most accurate in representing the unique behavior of Cu.

**Hint**: Analyze each option carefully to determine which reaction aligns with the unique properties of copper discussed.

### Final Answer:
The correct chemical change is the reaction of copper sulfate with NH4OH to precipitate copper hydroxide.