Question

what is a valence electron?
the sum of neutrons and protons.
a type of bond.
a popular compound.
the # of electrons in the last shell.

Explanation:

To determine the correct answer, we analyze each option:

• "The sum of neutrons and protons" refers to the mass number, not valence electrons.
• "A type of bond" is incorrect as valence electrons are related to electron configuration, not a bond type.
• "A popular compound" is irrelevant to the definition of a valence electron.
• "The # of electrons in the last shell" matches the definition of valence electrons (electrons in the outermost shell of an atom that participate in chemical bonding).

Answer:

The option (assuming the last option's text is "The # of electrons in the last shell"): The # of electrons in the last shell.