Which of the following forms a solid with non-directional covalent bonds?

A) neon
B) chlorine
C) copper
D) carbon
E) selenium

To determine which of the given elements forms a solid with non-directional covalent bonds, we need to understand the concept of covalent bonding and the nature of each element.

Covalent bonding occurs when two atoms share electrons in order to achieve a stable electron configuration. Non-directional covalent bonds are formed when there is equal electron sharing between atoms and there is no preferred direction for electron distribution.

Now, let's analyze each element:

A) Neon (Ne) - Neon is a noble gas that exists as a monatomic gas under normal conditions. Noble gases do not typically form covalent bonds with other elements, as they already have a stable electron configuration.

B) Chlorine (Cl) - Chlorine is a halogen gas that exists as a diatomic molecule (Cl2) under normal conditions. Chlorine can form covalent bonds, but it typically forms directional covalent bonds because the shared electrons are more attracted to the more electronegative chlorine atom.

C) Copper (Cu) - Copper is a metallic element that forms metallic bonds rather than covalent bonds. Metallic bonding involves a sea of delocalized electrons, which are free to move around and form a "sea of electron density," creating the characteristic properties of metals.

D) Carbon (C) - Carbon is a versatile element that can form many different types of bonds, including covalent bonds. Carbon is able to form non-directional covalent bonds, especially in its solid form, where it can arrange itself into a network structure, such as in diamond.

E) Selenium (Se) - Selenium is a nonmetal that can form covalent bonds, but these bonds are typically directional and occur in molecules or crystal structures.

Based on the explanation above, the only element that forms a solid with non-directional covalent bonds is:
D) Carbon (C)

Please note that the explanation provided is a general overview, and there may be exceptions or other factors that could affect the nature of the bond formed by each element.