What two elements have the same number of energy level (shells)?

Elements that are found in the same horizontal row (belong to the same period) in the periodic table, e.g. Fluorine and Neon both have the same energy level of 2.

Note: The question does not specify any two elements.

Explanation:

The modern periodic table is organized into eight vertical columns known as groups and seven horizontal rows known as periods. The atomic number ( number of protons in the nucleus) of elements increases when moving across the periodic table from left to right. The horizontal rows or periods represents an energy levels or the number of electron shells in an element. Energy levels (also called electron shells) are fixed distances from the nucleus of an atom where electrons may be found. Elements belonging to the same period have the same number of energy level or shells. For example, the elements belonging to Period 2 include lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon. These all have the same number of energy level of 2.

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