Force between two tiny charges

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Problem: Force between two tiny charges
Charges +2 μC and +3 μC are separated by 0.30 m in vacuum.
Question: Find their force magnitude.
Givens:
- q₁ = 2×10⁻⁶ C
- q₂ = 3×10⁻⁶ C
- r = 0.30 m
Assumptions: Point charges in vacuum; k = 9 × 10⁹ N·m²/C²; use centre-to-centre separation.
Choices (LaTeX):
A. 0.60\ \mathrm N
B. 0.18\ \mathrm N
C. 6\ \mathrm N
D. 0.054\ \mathrm N

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Tutoring approach:
Act as a patient physics tutor. Ask what I understand and what I have tried, then wait for my reply. Teach one step at a time; do not give the final answer or a complete solution immediately. Start with a physical picture. Define unfamiliar symbols and operators, explain signs and units, and state the model's assumptions. Give progressively stronger hints only when I need them. Ask me to predict a change before calculating it. When I finish, help me check dimensions and a limiting case, then ask one related transfer question. If information is missing or ambiguous, ask rather than inventing it. Distinguish exact results from approximations and acknowledge uncertainty.