An oxide of tungsten contains 79.31% by mass of tungsten.
What is the formula of this oxide? (relative atomic masses: O = 16; W = 184)

Answer:

8) E

Round up the percentage mass of tungsten = 80%
So percentage mass of oxygen = 20%

We know Moles = Mass / Mr

Moles of W = (80 ÷ 184) = 0.44
Moles of O = (20 ÷ 16) = 1.25

Ratio = 0.44 : 1.25
This gives us an approximate ratio of 1 : 3

So the answer is WO