the valency is the nomber of electrons gained , lost or shared by one atom to form a molecule with other atomsmonovalent : exhydrogen atom ( 1H ) the hydrogen atom contains one electron , so it can gain or share by one electron to complete the k level another exchlorine atom (35Cl17) the outermost energy level of chlorine atom contains 7 electrons , so it can gain or share by one electron to complete its outermost energy level to 8 electronsthen we can say monovalent the atom which gain or share by one electron Divalent : exoxygen atom ( 16O8) the outermost energy level of oxygen atom contains 6 electrons , so the atom can gain 2 electrons or share with 2 of it's electrons with 2 electrons fo : another oxygen atom to form oxygen molecule O2 two hydrogen atoms to form water molecule H2O.we can say atom which gain or share by 2 electrons is divalent Trivalent : exaluminium atom (27Al13) the outermost energy level of aluminium atom contains 3 electrons that can be lost during the chemical reactionExhydrogen is monovalent and noof valency is 1 (one) magnesium is divalent and noof valency is 2 (two) aluminium is trivalent and noof valency is 3 (three) lithium atomic no 3 , mass no7 , Li is monovalent can gain or share by 1( one ) electron I hope I can help you for best answer/
