Step 1: Using the Standard Cell Potential Formula
The standard cell potential is given by:
\[
E^\circ_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}}
\]
Here, Ce\(^{4+}/\)Ce\(^{3+}\) is the cathode and Co\(^{2+}/\)Co is the anode. Substituting values:
\[
1.89 = E^\circ_{\text{Ce}^{4+}/\text{Ce}^{3+}} - (-0.28)
\]
Step 2: Solving for \( E^\circ_{\text{Ce}^{4+}/\text{Ce}^{3+}} \)
\[
E^\circ_{\text{Ce}^{4+}/\text{Ce}^{3+}} = 1.89 + 0.28 = 2.17V
\]