Question

In which of the following systems will be radius of the first orbit (n=1) be minimum:

• A. Doubly ionized lithium
• B. Singly ionized helium
• C. Deuterium atom
• D. Hydrogen atom

Answer 1

Answer: (A)

Doubly ionized lithium

Answer 2

Radius of the orbit of an atom $r_n = 0.529 Å(\frac {n^2}{Z})$
Where Z is the atomic number.
For the first orbit n = 1
Then, $r_1 =\frac { 0.529 Å}{Z}$
⟹ $r_1​∝\frac{1}{Z}$
Since Z is at its maximum value in the case of doubly ionized lithium, this results in the smallest radius for the first orbit in doubly ionized lithium.

So, the correct option is (A): Doubly ionized lithium.