Question

Dry cell have short life span because of:

• A. oxidation of zinc cup
• B. acidic nature of $N{H}_{4}Cl$
• C. reduction of zinc cup
• D. due to presence of $Mn{O}_2$

Answer 1

Answer: (A), (B)

The correct options are
A oxidation of zinc cup
B acidic nature of $N{H}_{4}Cl$

Line art drawing of a dry cell: 1. brass cap, 2. plastic seal, 3. expansion space, 4. porous cardboard, 5. zinc can, 6. carbon rod, 7. chemical mixture.

A standard dry cell comprises a zinc anode, usually in the form of a cylindrical pot, with a carbon cathode in the form of a central rod. The electrolyte is ammonium chloride in the form of a paste next to the zinc anode. The remaining space between the electrolyte and carbon cathode is taken up by a second paste consisting of ammonium chloride and manganese dioxide, the latter acting as a depolarizer. In some designs, the ammonium chloride is replaced by zinc chloride.

Anode: $Zn⟶Zn+2e^{-}$

Cathode: ${2N{H}_4}^{+}+2e^{-}⟶2{NH}_3+H_2$

So at anode, oxidation of Zn takes place (zinc cup is used up and reduction of acidic $2{{NH}_4}^{+}$ takes place. Hence, the answer is A and B.