Which of the following diagrams does not represent a streamline flow?

1. 2.
3.   4.  
Hint: In a streamlined flow at any given point, the velocity of each passing fluid particle remains constant.

Explanation: If we consider a cross-sectional area, then a point on the area cannot have different velocities at the same time, hence two streamlines of flow cannot cross each other.
Hence, option (4) is the correct answer.