We have to find the ratio of area of triangle to that of rhombus, when they lie on the same base.
Let the triangle be ABC and the rhombus be ABDC.
Therefore, by using the properties of a rhombus that the diagonal divides the rhombus in two equal areas, we get
So, the ratio of the area of triangle to that of rhombus is 1 : 2.
Hence, the correct choice is option (b).