How does the crystalline structure of a metal differ from the structure of an ionic compound, such as sodium chloride or cesium chloride? (answer choices in picture above.)

The metal cube lattice is made of only one kind of atom.

Explanation:

As we know that metallic crystals are made up of only one kind of element.  A metal crystal is actually a huge sea of positive charges embedded in the layers of negative charges (electrons). The whole crystal is made up of same kind of atoms, e.g crystals of gold, crystals of iron.

If we talk about structure of metallic crystal, it can be body centered cubic, simple cubic, hexagonal or close cubic packing.

Now, coming towards the ionic crystals, we know that they are basically the crystals of ionic compounds like sodium chloride or cesium chloride. These crystals are formed due to ionic bonding between two or more than two kinds of elements/atoms. It is not possible for an ionic crystal to be composed of only one kind of atom. As far as structure is concerned, they can have different structure based on bonding between atoms in an ionic compound, e.g NaCl has octahedral geometry.

Therefore, it is very evident that best option is A.