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 correct chemical change involving copper, we will analyze each option based on the information provided in the video transcript.

### Step-by-Step Solution:

1. **Understanding Copper's Reactivity**:
- Copper (Cu) has a positive standard reduction potential (E°), which means it does not liberate hydrogen gas (H2) from non-oxidizing acids (like dilute sulfuric acid).
- It only reacts with oxidizing acids (like concentrated sulfuric acid and nitric acid).

2. **Analyzing the First Reaction**:
- **Reaction**: Cu + dilute H2SO4 → CuSO4 + H2
- Since dilute H2SO4 is a non-oxidizing acid, copper cannot react with it to liberate H2.
- **Conclusion**: This reaction is **not correct**.

3. **Analyzing the Second Reaction**:
- **Reaction**: Cu + dilute HNO3 → Cu(NO3)2 + N2O
- Dilute HNO3 is an oxidizing acid and can oxidize copper. However, the product stated is N2O, which is incorrect. The actual product is NO2.
- **Conclusion**: This reaction is **not correct**.

4. **Analyzing the Third Reaction**:
- **Reaction**: CuSO4 + KCN → K2CuCN4
- The correct reaction should yield K3Cu(CN)4, not K2CuCN4. The copper(II) ion reacts with cyanide to form a complex, but the stoichiometry is incorrect in the option.
- **Conclusion**: This reaction is **not correct**.

5. **Analyzing the Fourth Reaction**:
- **Reaction**: CuSO4 + NH4OH → Cu(OH)2 + (NH4)2SO4
- This is a basic double displacement reaction. The products are correctly stated as copper(II) hydroxide (Cu(OH)2) and ammonium sulfate ((NH4)2SO4).
- **Conclusion**: This reaction is **correct**.

### Final Answer:
The correct chemical change is:
**CuSO4 aqueous + NH4OH → Cu(OH)2 + (NH4)2SO4**

---