Question

Which of the following statement is incorrect for dry cell?

• A. Reaction at cathode $MnO _{2}+ NH _{4}^{+}+e^{-} \longrightarrow MnO ( OH )+ NH _{3}$
• B. Manganese is reduced from $+5$ to $+4$ state
• C. Cell potential is $1.5 V$
• D. Ammonia form complex with $Zn ^{2+}$ to give $\left[ Zn \left( NH _{3}\right)_{4}\right]^{2+}$

Answer 1

Answer: (B)

Anode $Zn (s) \longrightarrow Zn ^{2+}(a q)+2 e^{-}$
Cathode $MnO _{2}+ NH _{4}^{+}+e^{-} \longrightarrow MnO ( OH )+ NH _{3}$
At cathode manganese is reduced from $+4$ oxidation state to $+3$ oxidation state.
Ammonia produced in reaction form complex with $Zn ^{2+}$ to give $\left[ Zn \left( NH _{3}\right)_{4}\right]^{2+}$.
The cell has potential of $1.5\, V$.