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The nitride ion consists of:
[A] 7 protons + 10 electrons
[B] 10 protons + 10 electrons
[C] 7 protons + 7 electrons
[D] 10 protons + 7 electrons

Answer
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Hint: Nitride ion is an anionic species of the parent atom nitrogen. Nitride ions are formed when the nitrogen atom gains 3 electrons. The number of protons and electrons is equal in a neutral atom. Atoms with negative charge have excess electrons equal to their charge and atoms with positive charge have electrons deficiency equal to their charge.

Complete Step by Step Solution: We know that an atom consists of protons, electrons and neutrons. The protons and neutrons are in the nucleus of the atom and the electrons are in the orbitals surrounding the nucleus.
For an element, the atomic number tells us the number of electrons and protons in it. In a neutral state, the number of electrons is equal to the number of protons therefore the overall charge on the element is zero.
In the atom if the number of electrons exceeds the number of protons we see a negative overall charge on the atom and if the number of electrons is less than the number of protons, the overall charge becomes positive.
In the given question, we have nitride ion which is an anion formed by the nitrogen atom gaining three extra electrons, hence the overall charge on a nitride ion is -3.
We know that the atomic number of nitrogen is 7, which means in neutral state it has 7 electrons and 7 protons. But when it gains three electrons, which we can write as-$N+3{{e}^{-}}\to {{N}^{3-}}$, it becomes ${{N}^{3-}}$.
The nitrogen atom already had 7 electrons and 7 protons but nitrate ion has three extra electrons and the number of protons remains the same as addition of electrons does not affect the number of protons. Therefore, nitrate ions have (7+3) electrons and 7 protons.
Therefore, the correct answer is option [A] 7 protons + 10 electrons.

Note: The charge of a particle depends upon the number of electrons in it but the number of protons in an atom is always the same. However, the number of neutrons is not always equal to the number of protons. Atoms of the same elements can have different numbers of neutrons but the same number of protons. Such elements are called isotopes. For example, hydrogen has three isotopes-${}_{1}^{1}H$ (hydrogen) has no neutron,${}_{1}^{2}H$(deuterium) has one neutron and${}_{1}^{3}H$(tritium) has two neutrons.