d
The expression for magnetic field is given by,

\(B =\frac{\mu_{0} i }{2 r }\)

\(=\frac{\mu_{0}}{2 r} \times \frac{e V}{2 \pi r}\)

\(=\frac{\mu_{0} e V}{4 \pi r^{2}}\)

Calculate the potential as,

\(V =\left(2.18 \times 10^{6}\right)\left(\frac{1}{3}\right)\)

\(=7.3 \times 10^{5} m / s\)

Calculate the value of \(r\) as,

\(r=(0.529 \dot A )\left(\frac{3^{2}}{1}\right)\)

\(=7.461 \dot A\)

Substitute all values in the above expression as.

\(B =\frac{\mu_{0} eV }{4 \pi r ^{2}}\)

\(=\frac{\left(10^{-7}\right)\left(1.6 \times 10^{-19}\right)\left(7.3 \times 10^{5}\right)}{4.761 \times 4.761 \times 10^{-20}}\)

\(=0.0515 T\)