Select correct statement

Options

A. If salt bridge is removed, potential falls to zero
B. KCl cannot be used as electrolyte in salt bridge in case of silver electrode
C. Cell reaction is spontaneous if emf is positive
D. All of these

Answer

To solve the question regarding the correct statements about electrochemistry, we will analyze each statement one by one.

### Step-by-Step Solution:

**Step 1: Analyze the First Statement**
- The first statement claims that if the salt bridge is removed, then the potential falls to zero.
- **Explanation**: The salt bridge is essential for completing the circuit in an electrochemical cell. It allows the flow of ions, which is necessary for maintaining charge balance and enabling current flow. If the salt bridge is removed, the circuit is incomplete, and thus no current can flow, leading to a potential of zero.
- **Conclusion**: This statement is **true**.

**Step 2: Analyze the Second Statement**
- The second statement states that KCl cannot be used as an electrolyte in the case of a silver electrode.
- **Explanation**: When KCl is used in a solution with a silver electrode, a reaction occurs where silver ions (Ag⁺) react with chloride ions (Cl⁻) to form silver chloride (AgCl), which is an insoluble precipitate. This precipitation can block the electrode and hinder the electrochemical reaction.
- **Conclusion**: This statement is **true**.

**Step 3: Analyze the Third Statement**
- The third statement claims that a cell reaction is spontaneous if the EMF (Electromotive Force) is positive.
- **Explanation**: The spontaneity of a reaction is determined by the Gibbs free energy change (ΔG). A reaction is spontaneous when ΔG is negative. The relationship between ΔG and EMF is given by the equation ΔG = -nFE, where E is the EMF of the cell. If E is positive, ΔG will be negative, indicating that the reaction is spontaneous.
- **Conclusion**: This statement is **true**.

### Final Conclusion:
All three statements are correct based on the analysis above.