Question

A depolariser used in dry cell is
A) ammonium chloride
B) manganese dioxide
C) potassium oxide
D) sodium phosphate

Answer 1

Hint: In electricity, a battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. The dry cell is one of many general types of electrochemical cells. A dry cell has the electrolyte immobilized as a paste, with only enough moisture in it to allow current to flow. Unlike a wet cell, a dry cell can operate in any orientation without spilling, as it contains no free liquid. This versatility makes it suitable for portable equipment. By comparison, the first wet-cell batteries were typically fragile glass containers with lead rods hanging from an open top

Complete step by step solution:
The term "depolarizer" has been used to denote a substance used in a primary cell to prevent a buildup of hydrogen gas bubbles. A battery depolarizer takes up electrons during discharge of the cell, therefore it is always an oxidizing agent. Manganese dioxide is used in the dry cell as a depolarizer.
${\text{Mn}}{{\text{O}}_{\text{2}}}$ acts as the depolarizer and presents the buildup of hydrogen gas molecules
Anode : zinc container
Cathode: graphite rod surrounded by ${\text{Mn}}{{\text{O}}_{\text{2}}}$ poder
Electrolyte: paste of ${\text{N}}{{\text{H}}_{\text{4}}}{\text{Cl + ZnC}}{{\text{l}}_{\text{2}}}$
Cathode reaction :
${\text{2Mn}}{{\text{O}}_{\text{2}}}{\text{ + 2N}}{{\text{H}}_{\text{4}}}^{\text{+}}{\text{(aq) + 2}}{{\text{e}}^{\text{-}}} \to {\text{2M}}{{\text{n}}_{\text{2}}}{{\text{O}}_{\text{3}}}{\text{(s) + 2N}}{{\text{H}}_{\text{3}}}{\text{(g) + }}{{\text{H}}_{\text{2}}}{\text{O(l)}}$
Anode reaction
${\text{Zn}} \to {\text{Z}}{{\text{n}}^{{\text{2+}}}}{\text{ + 2}}{{\text{e}}^{\text{ - }}}$
${\text{Mn}}{{\text{O}}_{\text{2}}}$ acts as the depolarizer and presents the buildup of hydrogen gas molecules

Option “B” is correct

Note:
1. Electrolyte: A substance that, in solution or when molten, ionizes and conducts electricity.
2. Cathode: The electrode of an electrochemical cell at which reduction occurs.
3. Anode: The electrode of an electrochemical cell at which oxidation occurs.