Q.What is the action of selenium on magnesium metal?

Group 16 elements form EO2- and EO3-type oxides (E = S, Se, Te, Po) that are acidic, reacting with water to form the corresponding oxoacid (SO2+H2O -> H2SO3; SeO3+H2O -> H2SeO4); reducing power of the dioxides falls from SO2 (reducing) to TeO2 (oxidising). Group 17 elements form many, mostly unstable oxides: fluorine's OF2/O2F2 are strong fluorinating agents; chlorine's Cl2O/ClO2/Cl2O6/Cl2O7 are explosive oxidisers (ClO2 used for bleaching/water treatment); bromine's oxides are the LEAST stable of any halogen's (the 'middle row anomaly'); iodine's I2O5 is used to estimate carbon monoxide. Group 18 is inert to oxygen directly. Towards halogens, group 16 forms EX6 (octahedral, sp3d2, e.g. SF6), EX4 (see-saw, sp3d, e.g. SF4) and EX2 (bent, sp3, e.g. SCl2) halides, plus dimeric monohalides that disproportionate; stability falls fluoride > chloride > bromide > iodide. Group 17 elements combine with each other …