22. Choose the best description for a solid held together by London forces.

A. This substance melts at -30 °C to give a liquid that does not conduct electricity.
B. This substance melts at 650 °C and both the solid and liquid phases conduct electricity.
C. This substance melts at 390 °C to give a liquid that conducts electricity.
D. This substance melts at 1100 °C to give a liquid that does not conduct electricity.
E. This substance melts at 850 °C. The solid does not conduct electricity while the liquid does.

I would go with A.

The best description for a solid held together by London forces is option A. This substance melts at -30 °C to give a liquid that does not conduct electricity.

To determine the best description, we need to understand the properties of a solid held together by London forces.

London forces, also known as van der Waals forces, are weak intermolecular forces present between nonpolar molecules. They arise due to temporary fluctuations in electron distribution, resulting in temporary dipoles. These temporary dipoles induce similar temporary dipoles in neighboring molecules, causing attractive forces between them.

Based on this understanding, we can eliminate options B, C, D, and E because they mention properties that are not attributed to substances held together by London forces.

Option B states that both the solid and liquid phases conduct electricity. However, substances held together by London forces do not typically conduct electricity in either the solid or liquid state.

Option C mentions a substance that conducts electricity in the liquid state. Substances held together by London forces do not typically conduct electricity, even in the liquid state.

Option D describes a substance that melts at a high temperature and gives a liquid that does not conduct electricity. While substances held together by London forces generally have lower melting points, the electrical conductivity property mentioned is not consistent with substances held together by London forces.

Option E refers to a substance that melts at 850 °C, with the solid not conducting electricity but the liquid conducting electricity. Again, substances held together by London forces do not typically conduct electricity, even in the liquid state.

Therefore, option A is the best description as it aligns with the properties of a substance held together by London forces – melting at a relatively low temperature (-30 °C) and not conducting electricity in the solid or liquid state.