What is the equivalent resistance between $A$ and $D$ in the given circuit? (All resistors are $10 \,\Omega$)

In the circuit shown below,the ammeter reading is zero. Then the value of the resistance $R$ is (in $\Omega$)

In the given circuit diagram,a wire is joining points $B$ and $D$. The current in this wire is ............. $A$.

Two cells of voltage $10 \ V$ and $2 \ V$ and internal resistances $10 \ \Omega$ and $5 \ \Omega$ respectively,are connected in parallel with the positive end of $10 \ V$ battery connected to the negative pole of $2 \ V$ battery (figure). Find the effective voltage and effective resistance of the combination.

Write the necessary facts to understand Kirchhoff's laws.

The figure shows a network of five resistances and two batteries. Which of the batteries is getting charged?