A helium nucleus makes full rotation in a circle of radius 0.8 m in 2.5 seconds. The value of magnetic field B at the centre of the circle will be
A. 3.1 π × 10⁻²⁶ T
B. 2 π × 10⁻²⁶ T
C. 4 π × 10⁻²⁵ T
D. 2 π × 10⁻²⁵ T