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Given standard reduction potentials $E^{\circ}(\mathrm{Cu^{2+}/Cu}) = +0.34$ V and $E^{\circ}(\mathrm{Zn^{2+}/Zn}) = -0.76$ V, the standard EMF of the Daniell cell is:
A$+0.34$ V
B$+1.10$ V
C$+0.42$ V
D$-1.10$ V
Answer & Solution
Correct answer: B. $+1.10$ V
Cu is the cathode (higher reduction potential), Zn is the anode.
$E^{\circ}_{\text{cell}} = E^{\circ}_{\text{cathode}} - E^{\circ}_{\text{anode}} = (+0.34) - (-0.76) = +1.10$ V.
The positive value confirms the reaction is spontaneous as written. A common slip is to drop the negative sign on Zn, giving $+0.42$ V — option A is the trap.
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