Question

In which of the following systems will the radius of the first orbit be minimum?

• A. Hydrogen atom
• B. Deuterium atom
• C. Singly ionized Helium
• D. Doubly ionized Lithium

Answer 1

Answer: (D)

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.