JEE Advanced Physics: Chemical Bonding and Molecular Structure questions with solutions

Q1. The bond order of Be2 molecule is:

1. 0
2. 1
3. 2
4. 1/2

Answer: 0

Be2 has 4 electrons per Be atom, 8 total. MO filling order: sigma(1s)², sigma*(1s)², sigma(2s)², sigma*(2s)². Bonding electrons = 4 (in sigma1s and sigma2s). Antibonding electrons = 4 (in sigma*1s and sigma*2s). Bond order = (4-4)/2 = 0. Be2 does not exist as a stable molecule.