Figures below show regular hexagons, with charges at the vertices. In which of the following cases the electric field at the centre is not zero

Is electric field scalar or vector ? Why ?

In the given figure electric field at center $O$ due to section $AB$ of uniformly charged ring is $\overrightarrow E$. What will be electric field at $O$ due to section $ACB$ ?

Two charges $ + 5\,\mu C$ and $ + 10\,\mu C$ are placed $20\, cm$ apart. The net electric field at the mid-Point between the two charges is

Three charges are placed as shown in figure. The magnitude of $q_1$ is $2.00\, \mu C$, but its sign and the value of the charge $q_2$ are not known. Charge $q_3$ is $+4.00\, \mu C$, and the net force on $q_3$ is entirely in the negative $x-$ direction. The magnitude of $q_2$ is

Diagram shows symmetrically placed rectangular insulators with uniformly charged distributions of equal magnitude. At the origin, the net field net ${\vec E_{net}}$ is :-