Question

Which of the following statements are correct about a dry cell?

• [(I)] It is also known as Leclanche cell.

• [(II)] Electrolyte is a moist paste of \(NH_4Cl\) and \(ZnCl_2\).

• [(III)] Reaction at cathode is \[ MnO_2 + NH_4^+ + e^- \rightarrow MnO(OH) + NH_3 \]

• [(IV)] It can be charged.

• A. I, II, III only
• B. II, III, IV only
• C. I, III, IV only
• D. I, II, IV only

Hint:

Remember the simple rule:

• Dry cell = Primary cell = Not rechargeable.

• Lead-acid battery and Ni-Cd battery = Secondary cells = Rechargeable.
Whenever a question asks whether a dry cell can be charged, the answer is always No.

Answer 1

The Correct Option is A

Concept: A dry cell is one of the most common primary electrochemical cells used in flashlights, clocks, toys, remote controls, and many portable electronic devices. It is called a dry cell because the electrolyte is not present as a free-flowing liquid but as a moist paste. The commonly used dry cell is known as the

Leclanche cell. It converts chemical energy directly into electrical energy through spontaneous redox reactions. The important components of a dry cell are:

• Zinc container acting as the anode.

• Carbon rod acting as the cathode conductor.

• \(MnO_2\) acting as depolarizer.

• Moist paste of \(NH_4Cl\) and \(ZnCl_2\) acting as electrolyte.
Since a dry cell is a primary cell, the chemical reactions occurring inside it are irreversible. Therefore, it cannot be recharged.

Step 1: Examining Statement (I) Statement (I) says: ``It is also known as Leclanche cell.'' The commercial dry cell is indeed a modified version of the Leclanche cell. Historically, Georges Leclanche developed this type of cell, and therefore the dry cell is commonly referred to as the Leclanche cell. Hence, \[ \boxed{\text{Statement (I) is correct}} \]

Step 2: Examining Statement (II) Statement (II) states that the electrolyte consists of a moist paste of \[ NH_4Cl \quad \text{and} \quad ZnCl_2 \] In the dry cell, free liquid electrolyte is replaced by a paste containing: \[ NH_4Cl + ZnCl_2 \] This paste ensures ionic conductivity while preventing leakage. Therefore, \[ \boxed{\text{Statement (II) is correct}} \]

Step 3: Examining Statement (III) The cathode reaction occurring in the dry cell is \[ MnO_2 + NH_4^+ + e^- \rightarrow MnO(OH) + NH_3 \] The manganese dioxide acts as a depolarizer and gets reduced during cell operation. This equation correctly represents the reduction process occurring at the cathode. Therefore, \[ \boxed{\text{Statement (III) is correct}} \]

Step 4: Examining Statement (IV) Statement (IV) claims: ``It can be charged.'' A dry cell belongs to the category of primary cells. Primary cells undergo irreversible chemical reactions. Once the reactants are consumed, the cell becomes exhausted and cannot be restored to its original state by supplying electrical energy. Hence, dry cells are not rechargeable. Therefore, \[ \boxed{\text{Statement (IV) is incorrect}} \]

Step 5: Determining the correct combination From the above analysis: \[ (I) = \text{Correct} \] \[ (II) = \text{Correct} \] \[ (III) = \text{Correct} \] \[ (IV) = \text{Incorrect} \] Thus the correct set is \[ \boxed{I,\ II,\ III\ \text{only}} \] which corresponds to \[ \boxed{\text{Option (A)}} \]