There are many ways to test and identify metal. The easiest way is observing its color. Also how reflective it is. Other ways would be boiling point, melting point, density, or conductivity of the metal.
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Answer: 368 grams of sodium reacted.
Explanation:
The balanced reaction is :

According to stoichiometry :
2 moles of
are formed from = 2 moles of 
Thus 16 moles of
are formed from=
of 
Mass of 
Thus 368 grams of sodium reacted.