The correct answer is B. Na has fewer valence electrons than Mg.
Here's why:
1. When Na reacts with water, it loses one electron to achieve a stable electron configuration, becoming Na+.
2. This loss of an electron occurs because Na has one valence electron in its outer shell, making it easier for Na to donate this electron during the reaction.
3. On the other hand, Mg has two valence electrons in its outer shell, which requires more energy to remove compared to Na.
4. Due to the lower number of valence electrons in Na, it is more reactive with water than Mg, as the removal of one electron is energetically favorable for Na.
In summary, the statement that best explains why Na is more reactive with water is that Na has fewer valence electrons than Mg, making it easier for Na to donate an electron and react with water.
