What is the equivalent resistance between $A$ and $B$?

In a series connection of resistors,is the current equal or the voltage? And in a parallel connection of resistors,is the current equal or the voltage?

The effective resistance across $AB$ in the network shown is .......... $\Omega$.

What is the equivalent resistance across $A$ and $B$ in the figure shown,if $R = 3\,\Omega$?

The potential difference between the points $P$ and $Q$ in the circuit shown is: (in $\text{ V}$)

$A$ wire of resistance $R$ is bent to form a circular ring. Find the equivalent resistance between two points $X$ and $Y$ on its circumference. (The angle $XOY = \alpha$ is given.)