Which of the following is true for the figure showing electric lines of force? ($E$ is electrical field,$V$ is potential)

$A$ Van de Graaff generator produces:

Four charges are arranged at the corners of a square $ABCD$,as shown. The force on a $+ve$ charge kept at the centre of the square is

Two point positive charges are placed at a distance $d$ apart. $A$ third positive charge is placed at a distance $x$ on the perpendicular bisector. For what value of $x$ is the force on the third charge maximum?

Three point charges $Q, 4Q$ and $16Q$ are placed on a straight line of length $9 \text{ cm}$. The charges are placed in such a way that the system has minimum potential energy. Then:

Two tiny spheres carrying charges $1.5 \; \mu C$ and $2.5 \; \mu C$ are located $30 \; cm$ apart. Find the potential and electric field:
$(a)$ at the mid-point of the line joining the two charges,and
$(b)$ at a point $10 \; cm$ from this midpoint in a plane normal to the line and passing through the mid-point.