Electron-rich hydrides are compounds that contain excess electrons. These excess electrons are present as lone pairs. Lone pairs are pairs of electrons that are not involved in bonding with other atoms. They are located on an atom's valence shell and are not shared with another atom.

Explanation:
1. Electron-rich hydrides: These are compounds that have an excess of electrons compared to the number of electrons required for the compound to be stable.
2. Excess electrons: These are extra electrons that are not involved in bonding and are not required for the stability of the compound.
3. Lone pairs: These are pairs of electrons that are not involved in bonding and are located on an atom's valence shell. They are represented as a pair of dots in Lewis dot structures.
4. Dot structure: A dot structure is a diagram that represents the valence electrons of atoms in a molecule. The dots represent electrons, and the symbol of the element represents the nucleus and inner electrons. In the dot structure, the excess electrons in electron-rich hydrides would be represented as dots.
5. Free radical: A free radical is a molecule or atom that contains an unpaired electron. This is different from electron-rich hydrides, which have excess electrons in the form of lone pairs.
6. Chain pair: Chain pair is not a term used to describe the presence of excess electrons in electron-rich hydrides.
7. Lone pairs: Lone pairs are the correct answer because they accurately describe the presence of excess electrons in electron-rich hydrides.

In summary, electron-rich hydrides have excess electrons that are present as lone pairs. These lone pairs are not involved in bonding with other atoms and are represented as pairs of dots in Lewis dot structures.