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answers:
Travis say: B. Electrons
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Dr W say: The question is ridiculous.

here are the known stable isotopes for the first 20 elements
.. .. element.. .. .protons.... neutrons
... . . .. .H.. .. .. .. .. .1.. .. .. . .. .0 & 1
.. .. . .. .He.. .. .. .. ..2.. .. ... .. ..1 & 2
.. ... ... .Li. .. ... .. .. .3.. ... .. .. ..3 & 4
.. .. .. .. Be. ... . .. . .4..... ... ... .5
.. .. . .. .B.. .. ... .. .. 5.. ... .. .. ..5 & 6
.. .. .... .C.. ... .. .. .. 6.. .. .. .. ...6 & 7
.. .. .... .N.. ... ... .. ..7.. ... ... .. .7 & 8
.. .. .... .O.. ... ... .. ..8.. .. ... .. . 8 & 9 & 10
.. ... ... .F.. .. ... ... .. 9.. .. .. ... . 10 & 11 & 12
.. .. .. ...Na.. ... .. .. .11.. ... ... .. 12
.. ... ... .Mg.. ... .. .. .12.. ... .. .. .12 & 13 & 14
.. .. ... ..Al.. ... .. .. .. 13.. .. ... ... 14
.. ... .. ..Si.. .. .. ... .. 14.. ... ... .. 14 & 15 & 16
.. ... .. ..P.. ... ... ... ..15.. ... ... ... 16
.. .. .. .. S.. .. ... ... .. 16.. ... .. .. ..16 & 17 & 18 & 20
.. ... . .. Cl... ... ... ... 17.. ... ... .. .18 & 20
.. .. ... ..Ar.. ... ... .. ..18.. ... .. ... .18 & 20 & 22
.. .. .. .. K.. ... ... .. .. 19.. ... ... .. .20 & 22
.. ... .. . Ca.. ... ... .. .20.. ... .. .. ..20 & 22 & 23 & 24 & 26
beyond element 20, no isotopes exist where # protons = # neutrons

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so let's look at your choices

.. (A) in stable atom # protons = # nuclei
.. ... . NO.. all atoms have 1 nuclei. The # of protons can range from 1 to infinity
.. ... .. . . . ..we currently have discovered atoms with 1 to 118 protons
.. (B) in stable atom # protons = # electrons
.. ... . .NO.. .. if # protons = # electrons the atom has a net zero charge
. .. .. .. .. . . .. having a net zero charge doesn't mean the atom is stable
.. .. .. .. .. . .. .if # protons ≠ # electrons, the atom has a non-zero net charge
.. ... ... .. .. . . (in which case we would call the atom an ion)
.. .. .... .. . . ...having a non-zero charge doesn't mean the atom is stable or unstable
.. (C) in stable atom # protons = # neutrons
... .. . .NO... .you can see from the list above there are only 13 elements
.. .. .. .. .. . . .with known stable isotopes where # protons = # neutrons
.. (D) in stable atom # protons = # isotopes
.. .. . .NO.. .. .isotopes is how we distinguish atoms of the same element
.. .. ... ... .. .. .that have different numbers of neutrons. # of neutrons in any
.. .. ... .. .. .. . given element is free to vary from 0 to infinity. So # isotopes
.. .. .. .. .. .. . .can be 1 to infinity

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clearly (A), (C) and (D) are not viable choices.
In my humble opinion, neither is (B)

BUT.... your instructor might be part of a group of teachers that believe that once and atom gains or loses an electron, it's no longer an atom but an ion. And that ions and atoms are 2 different creatures. That's ridiculous in my opinion because electrons are shared and transferred and moved around all the time. If atoms stopped being atoms once then loose or gain electrons, atoms simply would not exist.

example.. my viewpoint
.. O.... is an oxygen atom
.. O(2-) is an oxygen atom with a non-zero net charge. it is ALSO an ion
some instructors say
.. O.. . is an oxygen atom
.. O(2-) is no longer an atom... it's an ION

you can see the difference in the image here
https://d2jmvrsizmvf4x.cloudfront.net/m4...
completely filled outer p orbital vs partially filled outer p orbital

In my opinion, ions of atoms are still atoms. They are a subset of atoms.
in some instructors opinions they are different animals completely.
why is that? because of this ridiculous definition
https://goldbook.iupac.org/html/A/A00493...
which states
.. " Smallest particle still characterizing a chemical element. It consists
.. of a nucleus of a positive charge (Z is the proton number and e the
.. elementary charge) carrying almost all its mass (more than 99.9%)
.. and Z electrons determining its size."
note that in the IUPAC definition, # protons = # electrons for the particle to be called an atom

this is a better definition
.. " Smallest particle still characterizing a chemical element. It consists
.. of a nucleus containing 1 or more protons surrounded by a field of electron density"

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IF... IF your instructor is a believer in that ridiculous IUPAC definition, then atoms (stable or unstable) must have equal number of protons and electrons. in which case "B" is the answer they are looking for
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pisgahchemist say: Number of protons....

The question makes no sense. When you use the term "stable" it refers to not undergoing radioactive decay, but it may have nothing to do with charge on the atom (ion). Only in elements with low atomic numbers is the number of protons and neutrons the same in a stable atom. As Z increases the mass number of stable isotopes increases faster. This means that most stable nuclei have more neutrons than protons.

Answer A and D are nonsense. Answer C would only apply to limited number of stable atoms. Answer B refers to a NEUTRAL atom. If the atom has no net charge, that is, it is not an ion, then the number of protons and electrons are the same. But "neutral" is not the same as "stable." It is possible to have lots of neutral atoms with unstable nuclei.

The bottom line: Whoever wrote your original question has no idea what they are talking about.
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xkdir say: cmzgurez
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