Question

Which of the following statement is not correct for a dry cell battery?

• A. Carbon(graphite) rod will act as cathode
• B. Zinc metal will act as a anode
• C. Ammonia produced in the cell reaction will forms a complex with $Z{n}^{2+}$
• D. Cell reaction will be reversed while passing current

Answer 1

The correct option is D Cell reaction will be reversed while passing current

Dry cell is a primary battery. In these batteries, chemical energy is converted into electrical energy as long as the chemical components are active.
Once the active chemical components are used up it becomes dead and cannot be reused again.
Thus, it cannot to recharged again for reusage.
Thus, statement (d) is incorrect.

In dry cell,
Zinc metal will act as anode and carbon (graphite) rod surrounded by powdered manganese dioxide and carbon will act as cathode.
The space between the electrodes is filled by a moist paste of ammonium chloride ($N{H}_{4}Cl$) and zinc chloride ($ZnC{l}_2$ ).
Cell reactions,
At anode:
$Zn\left(s\right)\to Z{n}^{2+}\left(aq\right)+2e^{-}$
At cathode:
$Mn{O}_2\left(s\right)+N{H}_4\left(aq\right)+e^{-}\to MnO\left(OH\right)\left(s\right)+N{H}_3\left(g\right)$

Ammonia produced in the reaction forms a complex with $Z{n}^{2+}$

$Z{n}^{2+}+4N{H}_3\to \left[Zn\right(N{H}_3{)}_4{]}^{2+}$

Cell potential of dry cell is $1.5V$
These cells are used in flashlights, radios, tape recorders, transistors, clocks, etc.
Thus, statement (a), (b) and (c) are correct.
thus statement d is not correct. Hence option d is correct.