$[A$ For $B>\frac{2}{3} \frac{p}{QR}$, the particle will re-enter region $1$
$[B]$ For $B=\frac{8}{13} \frac{\mathrm{p}}{QR}$, the particle will enter region $3$ through the point $P_2$ on $\mathrm{x}$-axis
$[C]$ When the particle re-enters region 1 through the longest possible path in region $2$ , the magnitude of the change in its linear momentum between point $P_1$ and the farthest point from $y$-axis is $p / \sqrt{2}$
$[D]$ For a fixed $B$, particles of same charge $Q$ and same velocity $v$, the distance between the point $P_1$ and the point of re-entry into region $1$ is inversely proportional to the mass of the particle
$\left(R^{\prime}-R\right)^2+R^2=R^{\prime}$
$\Rightarrow R^{\prime}=\frac{13}{8} R$
Assertion $(A)$ : In an uniform magnetic field, speed and energy remains the same for a moving charged particle.
Reason $(R)$ : Moving charged particle experiences magnetic force perpendicular to its direction of motion.

