Given data

• Battery voltage: $V = 4.2\,\text{V}$
• Battery capacity: $5800\,\text{mAh}$

Convert mAh to Ah $5800\,\text{mAh} = 5.8\,\text{Ah}$

Use energy formula Electrical energy in watt-hour is: $E = V \times (\text{Ah})$ $E = 4.2 \times 5.8 = 24.36\,\text{Wh}$

Convert Wh to joules We know: $1\,\text{Wh} = 3600\,\text{J}$ Hence, $E = 24.36 \times 3600 = 87696\,\text{J}$

Convert to kJ $E = 87.696\,\text{kJ} \approx 87.7\,\text{kJ}$

Match with options The correct option is: $\boxed{\text{A: }87.7\,\text{kJ}}$

Comparison with stored correct answer Stored correct answer: A

My derived answer is also A, so they agree.