Why is distilled water added to the crucible after igniting the magnesium metal?

To decompose the Mg3N and release ammonium gas

Explanation:

Distilled water is the pure state of water, without mixing with other substances and microorganisms. It is obtained through the distillation process. Even though it is clean water, it is not suitable for consumption, however it can have several other applications, such as being added to the crucible after ignition of the magnesium metal, because it allows the decomposition of Mg3N and release of ammonium gas, avoiding the emergence of explosions.

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periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.