Which of the following statements is false for Helmholtz coils?

The magnitude of magnetic induction at the mid-point $O$ due to the current arrangement as shown in the figure will be:

Find the magnetic field at $O$.

$A$ long straight wire carries a current along the $x$-axis. Consider the points $A(0, 1, 0)$,$B(0, 1, 1)$,$C(1, 0, 1)$,and $D(1, 1, 1)$. Which of the following pairs of points will have magnetic fields of the same magnitude?

$A$ long straight wire of radius $a$ carries a steady current $i$. The current is uniformly distributed across its cross-section. The ratio of the magnetic field at $a/2$ and $2a$ is:

An infinitely long wire carrying $1 \ A$ current in the $+z$ direction is placed at $(1 \ cm, 1 \ cm)$. Another wire carrying $1 \ A$ in the $+x$ direction is placed at $y=1 \ cm$. If the magnetic field due to this configuration at the origin is $B$. Let $B_0$ be the magnitude of the field if only the wire at $(1 \ cm, 1 \ cm)$ was present,then $\frac{B}{B_0}$ is