Atomic Structure

The radius of the nth Bohr orbit for a hydrogen-like species is given by:

where n is the principal quantum number, is the Bohr radius for hydrogen, and Z is the atomic number. For the 1st Bohr orbit of hydrogen (n = 1, Z = 1), .

We need to find a species where . Let us check the options:

• Option 1: n = 2, Li²⁺ (Z = 3):

• Option 2: n = 2, Be³⁺ (Z = 4):

• Option 3: n = 2, He⁺ (Z = 2):

• Option 4: n = 3, Li²⁺ (Z = 3):

Only option 2 gives the same radius as the 1st Bohr orbit of hydrogen.