Magnetic field at point $O$ due to the given structure is

Magnetic field at the centre $O$ due to the given structure is

Two thick wires and two thin wires, all of the same material and same length, form a square in three different ways $A, B$ and $C$ as shown in the figure. With correct connections shown, the magnetic field at the centre of the square is zero in case of

Which of the following materials obeys the nature of given voltage-current $(V-I)$ graph under constant temperature?

The direction of force on the charge -q moving in uniform magnetic field as shown in following figure towards