Oxygen is placed in the second period of the Mendeleev table.
Any element in the group 6 and period 3 (IUPAC version of periodic table).
The lightest element that is in period number 2 is lithium. Lithium is also the solid that is the least dense.
Period 2 (along with Lithium, Beryllium, Boron, Carbon, Nitrogen, Fluorine, and Neon.
Actinides
Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine, Neon.
Sulfur is a fourth period representative element that has similar properties to oxygen. Both elements belong to group 16 of the periodic table, also known as the oxygen group, and have similar chemical reactivity.
Magnesium
Neon
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Chlorine is an element in the same period as fluorine. Both elements are located in period 2 of the periodic table. They exhibit similar chemical properties due to being in the same period.
Calcium
Any element in the group 6 and period 3 (IUPAC version of periodic table).
In the same period as oxygen (O), you will find elements such as nitrogen (N), fluorine (F), and neon (Ne) on the periodic table.
The lightest element that is in period number 2 is lithium. Lithium is also the solid that is the least dense.
The only element out of those listed which is on the same row of the periodic table as phosphorus is magnesium.
Magnesium
Period 2 (along with Lithium, Beryllium, Boron, Carbon, Nitrogen, Fluorine, and Neon.