Current flows through uniform,square frames as shown. In which case is the magnetic field at the centre of the frame not zero?

Two circular coils $X$ and $Y$,having an equal number of turns,carry equal currents in the same sense and subtend the same solid angle at point $O$. If the smaller coil $X$ is midway between $O$ and $Y$,then if we represent the magnetic induction due to the bigger coil $Y$ at $O$ as $B_Y$ and that due to the smaller coil $X$ at $O$ as $B_X$,then:

The figure shows a circular coil carrying current $i$ kept very close but not touching at a point $A$ on a straight conductor carrying the same current $i$. The magnitude of magnetic induction at the centre $O$ of the circular coil will be:

$A$ uniform beam of positively charged particles is moving with a constant velocity parallel to another beam of negatively charged particles moving with the same velocity in the opposite direction,separated by a distance $d$. The variation of the magnetic field $B$ along a perpendicular line drawn between the two beams is best represented by:

One Tesla is equal to

Mark the correct statement.