If $r_0$ is radius of first orbit in Hydrogen atom then radius of first orbit in Hydrogen like atoms is given by $r=\frac{r_0}{Z}$.
For Hydrogen, $Z=1$
For Deuterium, $Z=1$
For singly ionized Helium $H{e}^{+}$, $Z=2$
For doubly ionized Lithium $L{i}^{2+}$, $Z=3$

$\therefore$ Radius of the first orbit, $r$ is minimum for doubly ionized Lithium.