In the given circuit,if no current flows through the ammeter,what is the value of $X$ in $\Omega$?

$A$ uniform wire of length $200 \, cm$ is connected to a battery, two resistors and a galvanometer as shown in the figure. The galvanometer shows null deflection when the jockey $J$ is at $80 \, cm$ from point $A$. If the resistor $R_2$ is shunted with $30 \, \Omega$ resistance, the galvanometer shows null deflection when the jockey $J$ is at $100 \, cm$ from point $B$. Then the values of $R_1$ and $R_2$ respectively are

Potential difference between $A$ and $B$ is .............. $V$.

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

In the circuit shown,what is the potential difference $V_{PQ}$?

The potential difference between the points $A$ and $B$ is nearly: (in $V$)