Which of the following figure shows the magnetic flux density $B$ at a distance $r$ from a long straight rod carrying a steady current $i$?

Two long thin wires $ABC$ and $DEF$ are arranged as shown. The magnitude of the magnetic field at $O$ is

A circular conductor, of uniform resistance per unit length, is connected to a battery of $4 \mathrm{V}$. The total resistance of the conductor is $4 \mathrm{\Omega }$. The net magnetic field at the centre of the conductor is

The magnetic field $B$ at $O$ due to current carrying loop placed in the $x-y$ plane as shown in the figure is