Which of the following figures correctly depicts the direction of the magnetic field of a current-carrying coil?

$A$ circular loop of radius $r$ of conducting wire connected with a voltage source of zero internal resistance produces a magnetic field $B$ at its centre. If instead, a circular loop of radius $2r$, made of the same material and having the same cross-section, is connected to the same voltage source, what will be the magnetic field at its centre?

Two long parallel wires are at a distance $R$ apart. They carry steady equal currents in the same directions as shown in the figure. The ratio of magnetic fields at $A, B$ and $C$ respectively,is

$A$ wire of length $l$ is bent into a circular coil of one turn of radius $R_1$. Another wire of the same material and same area of cross-section and same length is bent into a circular coil of two turns of radius $R_2$. When the same current flows through the two coils, the ratio of magnetic induction at the centres of the two coils is

The $SI$ unit of magnetic permeability is

The magnetic field at the centre $C$ of the circular arc is: