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

Options

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

Answer

C

Explanation

Radius of nth bohr's orbit of hydrogen like atom,
`r_(n)prop(n^(2))/(Z)`
Where, Z is atomic number.
For first orbit, `n=1`
`therefore r_(n) prop (1)/(Z)`
Now, for radius of first orbit to be minimum, its atomic number must be greater.
Here in the problem, atomic number Z is greater for doubly ionised lithium and is Z=3. hence, for this system the radius of first orbit will be minimum.