One of the elements predicted by D.I. Mendeleev, forms an oxide, the mass fraction of oxygen in which is 0.305.

One of the elements predicted by D.I. Mendeleev, forms an oxide, the mass fraction of oxygen in which is 0.305. The element exhibits an oxidation state of +4 in this oxide. Determine the relative atomic mass of this element and name it.

The oxide formula of an element with an oxidation state of +4 looks like this: XO2. Knowing the relative atomic mass of oxygen and its mass fraction in the oxide, we calculate the molar mass of the oxide:

32: 0.305

The fraction of the second element is 1 – 0.305 = 0.695, and its relative atomic mass is calculated as 0.65 * (32: 0.305) = 72.93

This is germanium (Ge) predicted by Mendeleev as ekasilicon, an analogue of silicon.