What number is given to magnesium in the periodic table?

Magnesium, abbreviated as Mg, is an element with the atomic number 12. 
Magnesium is an alkaline earth metal which is solid at 20 degrees centigrade, strongly basic, and has a hexagonal crystal structure. To the naked eye, magnesium is a somewhat reflective, silvery substance. Magnesium also has an atomic weight of 24.305, a melting point of 650 degrees centigrade, and a boiling point of 1090 degrees centigrade.
This mineral is found readily in seawater, soil, and even a number of foods! Humans need magnesium in their diet and typically get it through eating dark, leafy greens, nuts, and bananas. 
When handling magnesium in a laboratory or industrial setting, be careful when opening containers of chip or powdered magnesium as there is the potential for spontaneous ignition on contact with wear. Though magnesium does not pose any serious health risks, wear a face mask and gloves to protect the airways and hands. Accumulation of magnesium dust in the lungs or stomach can cause flu-like symptoms.
https://www.britannica.com/science/magnesium