A force F\=7i^+3j^N acts at r\=−2i^+1j^m. What is the magnitude of the torque about the origin?
τ = r×F = |i^j^k^−210730| = k^((−2)×3−1×7) = k^(−6−7) = −13k^Nm. Magnitude = 13Nm. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 13 Nm. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.
Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.