A particle that contains 9 protons, 10 neutrons and 10 electrons is

Analyze the question: We're given the number of protons, neutrons and electrons in a particle, and we must decide what kind of particle it is.

Concept:

• Protons carry a positive charge (+1 each).
• Electrons carry a negative charge (-1 each).
• Neutrons carry no charge.
• Net charge = number of protons − number of electrons.
• If protons = electrons, the particle is a neutral atom.
• If electrons > protons, it is a negative ion (anion).
• If protons > electrons, it is a positive ion (cation).

Solution:

• Protons = 9, so the positive charge is +9.
• Electrons = 10, so the negative charge is -10.
• Net charge = +9 + (-10) = -1

The particle has one more electron than protons, so it carries a single negative charge.

The atomic number is 9, which is fluorine (1s² 2s² 2p⁵). The particle is the fluoride ion, F⁻, with mass number 9 + 10 = 19. Fluorine is a non-metal, and non-metals gain electrons to form negative ions, which fits perfectly.

Answer: D, negative ion

Tip: Compare protons and electrons first, ignoring the neutrons. They are only there to distract you, since they affect the mass number but not the charge. More electrons means negative, and more protons means positive. A memory aid is "Anion = A Negative ION", and electrons are the extra ones in an anion.