when looking at periods, which of the following are increasing?

reactivity
atomic mass
energy level
none

When looking at periods, Energy level  is increasing

Explanation:

The elements which is present in the periodic table kept in the increasing atomic number. It can follow periodic law and also periodic formation but the formation of table can be used by several types where it is predicted by physical, chemical and also the atomic properties.

According to Mendeleev properties of elements are put into the proper Column. It is generally kept by increasing the atomic mass but in 1911 Mosely arranged the periodic table where he kept it according to their mass.

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