Final answer:
To make quadrilateral QRST a rhombus, the ratio D^2/d^2 should be 2.25.
Step-by-step explanation:
A rhombus is a quadrilateral in which all four sides have the same length. In order for quadrilateral QRST to be a rhombus, the value of n must satisfy the condition that the lengths of the vectors closest to R and T are equal. This can be represented as qr/d^2 = qt/d^2, where qr and qt are the charges on R and T, and d is the distance.
Similarly, the vectors closest to S must also have the same length as those near R and T. This can be represented as qs/D^2 = qr/d^2, where qs is the charge on S, D is the distance, and d is the distance.
Therefore, to make quadrilateral QRST a rhombus, the ratio D^2/d^2 should be 2.25.