Question

How can we find that the oxide formuale belong to the particular group

Answer 1

first u should know the valency of the metal or non metal whose oxide u r forming

suppose , for magnesium whose valency is 2 , the oxide formula will be MgO oxygen has a valency of 2 and magnesium also has valency as 2 thus the no. 2 will be cancelled out .

for sodium whose valency is 1 will be Na2O  [ valency of oxygen will go with sodium  and that of sodium will come with oxygen ..no need to write 1 if the valency of an element is 1 ]

for aluminium whose valency is 3 will be Al2O3

i tried my best to explain hope u will understand