The x – y plane is the plane of a couple of 25 Nm magnitude and $\hat{i}, \hat{j} , \hat{k}$ are unit vectors along x, y, and z directions respectively. Which one of the following represents the couple vector?
(a) $\frac{25}{12}\hat{i}+\frac{25}{12}\hat{j}$ Nm
(b) 25 $\hat{i}$
(c) 25 $\hat{j}$
(d) 25 $\hat{k}$