The answer to this is 22, confirmed by gradpoint
By determining the period that the element is in. For example, Calcium is in period 2 therefore its valence electron is located on energy level 2.
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Lithium has 1 valence electron and chlorine has 7 valence electrons.
Answer:
Equation 2, because K being more reactive, exchanges position with Pb in PbNO3.
Explanation:
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In this case, according to the given reactions, it is possible to realize that according to the reactivity series, since K is is group 1A of alkali metals, we infer it is by far more reactive than magnesium, for that reason last two choices can be easily discarded. Now, considering equation 2, it would be necessary to complete it to figure out the correct option:
Whereas it can be seen that potassium exchanges position with Pb according to the double displacement reaction; therefore, the correct answer is "Equation 2, because K being more reactive, exchanges position with Pb in PbNO3".
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