$A$ student has $10$ resistors of resistance $r$. The minimum resistance made by him from given resistors is

$A$ piece of wire of resistance $4\,\Omega$ is bent through $180^o$ at its mid-point and the two halves are twisted together. The new resistance is ............ $\Omega$.

In the given circuit,the equivalent resistance between $A$ and $B$ is ....... $\Omega$.

Equivalent resistance of the following network is . . . . . . $\Omega$.

How can resistors be connected? Explain.

Five identical resistors are initially arranged as shown in the figure by solid lines. If two identical resistors are added as shown by the dashed lines,the change in the equivalent resistance between the initial and final configurations is ....... $\Omega$.