Concept:
The magnetic field inside a toroid is
\[
B=\frac{\mu_0NI}{2\pi r},
\]
where
\[
N=\text{number of turns},
\quad
I=\text{current},
\quad
r=\text{mean radius of the toroid}.
\]
Step 1: Write the given data.
\[
N=1000,
\qquad
I=1\,A,
\qquad
r=\frac{\mu_0}{\pi}.
\]
Step 2: Substitute into the toroid field formula.
\[
B
=
\frac{\mu_0(1000)(1)}
{2\pi\left(\frac{\mu_0}{\pi}\right)}.
\]
\[
=
\frac{1000\mu_0}
{2\mu_0}.
\]
\[
=
500.
\]
Hence,
\[
B=500\,T.
\]
Step 3: Identify the correct option.
\[
\boxed{B=500\,T}
\]
Therefore,
\[
\boxed{\text{Answer = (A)}}
\]