This problem is providing us with the end of the electron configuration an element as s²p⁴ and asks for the most commonly formed ion. At the end, the answer is b Y²⁻.
In chemistry, when analyzing electron configurations, one must first take into account how the energy levels must be filled with electrons.
Now, note the problem states that the electron configuration ends by s²p⁴, which means it is closer to complete the octet so it needs two electrons in order to do so, as it behaves as a nonmetal.
Therefore, the most commonly ion formed by this element is Y²⁻, because of the fact that it needs two electrons to complete the octet and thus become chemically stable and likely to bond with a metal.
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