What are the advantages of the null-point method in a Wheatstone bridge? What additional measurements would be required to calculate $R_{\text{unknown }}$ by any other method?

In the Wheatstone bridge (shown in the figure) $X=Y$ and $A>B$. The direction of the current between $\mathrm{ab}$ will be

The figure shows a circuit diagram of a Wheatstone bridge to measure the resistance $G$ of the galvanometer. The relation $\frac{P}{Q}=\frac{R}{G}$ will be satisfied only when

In the circuit shown, a meter bridge is in its balanced state. The meter bridge wire has a resistance $0.1 \mathrm{ohm} {\mathrm{cm}}^{-1}$. The value of an unknown resistance $X$ and the current drawn from the battery of negligible resistance is

In a practical Wheatstone bridge circuit as shown, when one more resistance of $100 \mathrm{\Omega }$ is connected in parallel with an unknown resistance $x$, then ratio $l_1/l_2$ become $2. l_1$ is balance length and $AB$ is a uniform wire. Then value of $x$ must be: