Construct an Ampere’s loop in the concerned regions to see the value of $i_p$.
At a pont outside the co-axial tube at a diatance R from the central axis consider a circular path.
Then from Amperes Law closed integral of $B .dl=\mu_0 I(net)$
but the net current is zero as the current in the two cables flow in opposite directions.
therefore Magnetic field is zero outside
Ans : (a)