A metal oxide has a relative formula mass (Mr ) of 81. The formula of this metal oxide is MO. Given that the relative atomic mass (Ar ) of oxygen is 16, what is the metal in the metal oxide?

The formula of the metal oxide is MO, which means there is only one oxygen atom bonded to the metal. The Mr of a compound is the sum of Ar of the elements that make up the compound. So, from this we can construct a equation.

Mr of MO = Ar of oxygen + Ar of metal

81 = 16 + Ar of metal

We can then rearrange the equation to give the Ar of the metal.

Ar of metal = 81 - 16

Ar of metal = 65

By looking at a periodic table we can see that the metal that has an Ar of 65 is Zinc.