In the given current distribution,what is the value of $I$ in $A$?

In the circuit shown in the figure,all the resistances are identical and each has the value $r \ \Omega$. The equivalent resistance of the combination between the points $A$ and $B$ will remain unchanged even when the following pairs of points marked in the figure are connected through a resistance $R$.

If the Wheatstone bridge shown in the figure is balanced,then the values of $R_1$ and $R_2$ are ...... $\Omega$ and ...... $\Omega$ respectively.

The equivalent resistance between points $A$ and $B$ is ............ $\Omega$.

Why is the circuit configuration known as a Wheatstone bridge?

Five resistors,each of resistance $R$,are arranged as shown in the figure. $A$ battery of voltage $V$ is connected between points $A$ and $B$. Find the current flowing through the branch $AFCEB$.