Atomic Structure

Li, Be, B, and C are elements of the second period. Across a period from left to right, the atomic radii generally decrease. This is because as we move across a period, the number of protons in the nucleus increases, increasing the effective nuclear charge. This stronger positive charge pulls the electrons in the outermost shell closer to the nucleus, resulting in a smaller atomic radius.

Li (Lithium) is in group 1. Be (Beryllium) is in group 2. B (Boron) is in group 13. C (Carbon) is in group 14.

Therefore, the atomic radii decrease in the order:

The energy and radius of the first Bohr orbit are given by the following formulas:

1. The energy of the nth orbit for a hydrogen-like atom:

   Where is the atomic number of the ion.

2. The radius of the nth orbit:

For Li²⁺ (Z = 3) and He⁺ (Z = 2), we calculate for (the first Bohr orbit).

• For Li²⁺ (Z = 3):

• For He⁺ (Z = 2):

Thus, the correct values are:

Therefore, the correct answer is (1).