Determine the bond order in a molecule or ion with 10 valence electrons.

Bond order = 1

Explanation:

The 10 valence electrons can be added across bonding and antibonding molecular orbitals (MO) in a manner shown below:

- two 1s orbitals combine to form σ1s and σ*1s with 2 electrons in each MO

- the 3 p-orbitals combine to form σ2pz, σ*2pz with 2 electrons in each MO. In addition a degenerate π2py, π2px and π*2py, π*2px with a total of 4 electrons in each set of degenerate orbitals

Based on the energy level ordering the 10 electrons can be distributed across the bonding MO's as follows

(σ1s)²<(σ*1s)²<(σ2s)²<(σ*2s)²<(π2py)¹ = (π2px)¹

Bond order = 1/2(Bonding electrons - non-bonding electrons) = 6-4/2 = 1

c is the answer because when something is left after something evaporates that shows the chemical change.