The highest oxide of an element expressed by the general formula EO2.

The highest oxide of an element expressed by the general formula EO2. The mass fraction of oxygen in it is 36% What element is it. Write the equations of interaction with HCl

To solve this problem, you need to use the formula to calculate the mass fraction of an element in a substance.
Given:
W (O) = 36% or 0.36
EO2 -? Decision.
W = Ar * n / Mr, where:
W – mass fraction of the element,
Ar is the relative atomic mass of the element,
Mr- is the relative molecular weight,
n is the number of atoms.
0.36 = 16 * 2 / Mr
M r = 32 / 0.36 = 88.8
Mr (EO2) = 88.8 means Ar (E) = 88.8 – 32 = 56.8, which means this element is iron (Fe)
Iron reacts with acids to form a salt, with an oxidation state of +2.
Fe + 2HCl = FeCl2 + H2