A uniform rod of mass m and length l is struck at one end by a...

The angular impulse provided by the force about the centre of mass is equal to the change in angular momentum of the rod about its centre of mass.

The torque acting on the rod about its centre of mass is $\tau = F \times \dfrac{l}{2}$.

The angular impulse is given by $J = \tau t = F \left(\dfrac{l}{2}\right) t = \dfrac{Flt}{2}$.

Since the initial angular momentum is zero, the final angular momentum $L$ is equal to the angular impulse.

Thus, $L = \dfrac{Flt}{2}$.