Correct answer is (C) 4 units
A(0,3), O(0,0) and B(5,0) are the three vertices of a rectangle;
let C be the fourth vertex Then, the length of the diagonal,
\(AB=\sqrt{(5-0)^2+(0-3)^2}\)
= \(\sqrt{(5)^2+(-3)^2}\)
= \(\sqrt{25+9}\)
= \(\sqrt{34}\) units
Since, the diagonals al rectangle is equal.
Hence, the length of its diagonals is \(\sqrt{34}\) units.