Chromate and dichromate ions respectively are

Options

A. `CrO_4^(2-)` and `Cr_2O_7^(2-)`
B. `Cr_2O_7^(2-)` and `CrO_4^(2-)`
C. `CrO_4^(2-)` and `Cr_2O_5^(2-)`
D. `Cr_2O_5^(2-)` and `CrO_4^(2-)`

Answer

To answer the question about the chromate and dichromate ions, we need to identify their chemical formulas and understand their composition. Here’s a step-by-step solution:

### Step 1: Understand the Composition of Chromate Ion
- The chromate ion consists of chromium (Cr) and oxygen (O) atoms.
- The chemical formula for the chromate ion is CrO₄²⁻.
- This indicates that there is one chromium atom and four oxygen atoms, and the ion carries a charge of -2.

### Step 2: Understand the Composition of Dichromate Ion
- The dichromate ion also consists of chromium (Cr) and oxygen (O) atoms, but in a different ratio.
- The chemical formula for the dichromate ion is Cr₂O₇²⁻.
- This indicates that there are two chromium atoms and seven oxygen atoms, and the ion also carries a charge of -2.

### Step 3: Summarize the Information
- Chromate Ion:
- Formula: CrO₄²⁻
- Composition: 1 Chromium atom, 4 Oxygen atoms, Charge: -2
- Dichromate Ion:
- Formula: Cr₂O₇²⁻
- Composition: 2 Chromium atoms, 7 Oxygen atoms, Charge: -2

### Final Answer
- Chromate ion is CrO₄²⁻ and dichromate ion is Cr₂O₇²⁻.