The compound used for gravimetric estimation of `Cu(II)` is:

Options

A. `Cu_2(SCN)_2`
B. `Cu_2O`
C. `Cu_2l_2`
D. `Cu_2CO_3`

Explanation

To solve the question regarding the compound used for the gravimetric estimation of Cu(II), we can follow these steps:

### Step 1: Understand the Concept of Gravimetric Estimation
Gravimetric estimation involves the measurement of mass to determine the quantity of an analyte (in this case, Cu(II)) in a sample. This usually requires the formation of a stable compound that can be isolated and weighed.

**Hint:** Gravimetric methods often rely on the precipitation of a compound that contains the element of interest.

### Step 2: Identify the Relevant Reactions
When estimating Cu(II) ions, we need to identify the compounds that can react with Cu(II) to form a precipitate. Commonly, thiocyanate ions (SCN⁻) are used to form copper thiocyanate (CuSCN).

**Hint:** Look for compounds that can react with Cu(II) to form a solid precipitate.

### Step 3: Write the Reaction
The reaction for the formation of copper thiocyanate can be written as follows:
\[ \text{Cu}^{2+} + 2 \text{SCN}^- \rightarrow \text{Cu(SCN)}_2 \]

This indicates that when copper ions react with thiocyanate ions, they form a complex that can be precipitated.

**Hint:** The stoichiometry of the reaction will help in understanding the amount of precipitate formed.

### Step 4: Evaluate the Options
From the options provided in the question, we need to identify which compound corresponds to copper thiocyanate. The correct compound for gravimetric estimation of Cu(II) is copper thiocyanate (CuSCN).

**Hint:** Compare the chemical formulas of the options with the known formula of copper thiocyanate.

### Step 5: Conclusion
After evaluating the options, we conclude that the compound used for gravimetric estimation of Cu(II) is indeed copper thiocyanate (CuSCN).

**Final Answer:** The compound used for gravimetric estimation of Cu(II) is **copper thiocyanate (CuSCN)**.