To determine which molecule has a single pair of nonbonding electrons on the central atom, we need to analyze the Lewis structures of each option. Let's examine each molecule in detail:
a. CO₂ (Carbon dioxide)
The central atom here is carbon (C). In the Lewis structure of CO₂, carbon forms two double bonds with oxygen atoms. Carbon does not have any lone pairs (nonbonding electrons). Hence, CO₂ does not have a single pair of nonbonding electrons on the central atom.
b. CH₄ (Methane)
The central atom here is carbon (C). In methane, carbon forms four single bonds with four hydrogen atoms. There are no lone pairs of electrons on the carbon atom. Therefore, CH₄ does not have a single pair of nonbonding electrons on the central atom.
c. PH₃ (Phosphine)
The central atom here is phosphorus (P). In phosphine, phosphorus forms three single bonds with three hydrogen atoms and has one lone pair of electrons. Therefore, PH₃ has a single pair of nonbonding electrons on the central atom.
d. H₂O (Water)
The central atom here is oxygen (O). In water, oxygen forms two single bonds with two hydrogen atoms and has two lone pairs of electrons. Therefore, H₂O has two pairs of nonbonding electrons on the central atom, but not just one.
e. C₂H₄ (Ethylene)
The molecule has two central carbon (C) atoms. In ethylene, each carbon atom forms a double bond with another carbon atom and single bonds with two hydrogen atoms. Neither of the carbon atoms has lone pairs. Thus, C₂H₄ does not have a single pair of nonbonding electrons on the central atoms.
From the above analysis, we conclude that the molecule with a single pair of nonbonding electrons on the central atom is:
c. PH₃ (Phosphine)
So, the correct answer is c. PH₃.
