Final answer:
CuO is the molecule among the listed options as it consists of chemically bonded copper and oxygen atoms. Lattice energy is influenced by the size and charge of the ions involved, with smaller and more highly charged ions resulting in higher lattice energies.
Step-by-step explanation:
The molecule among the listed options is CuO. A molecule is defined as two or more atoms that are chemically bonded together. CuO, or copper(II) oxide, consists of copper (Cu) and oxygen (O) atoms that are bonded covalently, thus forming a molecule. The other options such as C (carbon), Mg (magnesium), and Li (lithium) are individual elements, not compounds or molecules.
Concerning lattice energy comparison for various compounds, lattice energy is generally higher in ionic solids with smaller, more highly charged ions. As examples:
MgO would have a higher lattice energy than MgSe due to the smaller size and greater charge on the oxygen ion compared to the selenium ion.
LiF would have a higher lattice energy than MgO as the smaller Li+ ion can pack more tightly with the F- ions compared to the larger Mg2+ ions with oxygen.
Looking at K₂O versus Na₂O, K₂O has a lower lattice energy than Na₂O due to the larger size of the K+ ion compared to the Na+ ion.