Answer:

Neon

Explanation:

Elements are arranged in a certain order in a table known as the periodic table of elements, and they are arranged in groups and periods with similar properties to each other. Earlier in history when Dmitri Medeleev created the first periodic table, some spaces were left open because many elements had not been discovered, however using this table, the properties of these elements could be predicted, even though the had not been discovered.

In period 2 of the periodic table, the mass of each element increases from left to right. Hence, it can be seen that out of the elements in period 2, lithium (Li) has the lowest mass, and neon (Ne) has the highest mass.