b
The current flowing clockwise in an equilateral triangle has a magnetic field in the direction of \(\hat{ k }\)

\(\tau=\operatorname{BiN} A \sin \theta\)

\(\tau=\operatorname{BiN} A \sin 90^{\circ}\)

\(\tau= Bi \times \frac{\sqrt{3}}{4} I ^{2} \times 1\)

\(\left[\because\right.\) Area of equilateral triangle \(=\frac{\sqrt{3}}{4} I ^{2}\) and \(\left. N =1\right]\)

\(\Rightarrow I ^{2}=\frac{4 \tau}{\sqrt{3} Bi } \Rightarrow I =2\left[\frac{\tau}{ Bi \sqrt{3}}\right]^{1 / 2}\)