Look at the periodic table to find the charge on atoms.
Magnesium is +2 and Nitrogen is -3. Since there are two nitrogen charge 2*-3 = -6 there needs to be 3 Mg then (3*2+ = 6+) to pair with the two nitrogen.
3 Mg(+2) + 2 N(-3) = Mg3N2
F BLOCK is the block on the period table that contains the actinide series of elements.
Actinide series of elements are two rows under the periodic table which include Lanthanide series and Actinide series. These are all radioactive elements and all of these are not not found in nature. All these are included in F block element.