Which diagram correctly illustrates the path of light rays through the rectangular block?

The main diagram shows parallel light rays entering from the left. These rays pass through two converging elements (triangular shapes), which cause them to converge. After the second converging element, the rays are strongly converging as they enter a rectangular block. Inside this block, the rays continue to converge, cross at a focal point, and then diverge as they exit the block to the right.

The question asks to identify the pattern of light rays within the rectangular block. This means we are looking for a diagram that shows rays entering the block, converging, crossing over, and then diverging as they exit.

• Diagrams 1, 2, 4, and 6 show various patterns, but none clearly depict the converging-crossing-diverging behavior expected within the block. They show mostly parallel or slightly distorted parallel lines.
• Diagram 3 shows rays converging towards a central empty square and then diverging. This implies an obstruction or a different optical element, not just light passing through a uniform block.
• Diagram 5 shows light rays entering from the left, converging towards a central point within the block, crossing over at that point, and then diverging as they exit to the right. This pattern perfectly matches the behavior of light rays that have been focused and are passing through a medium where their focal point is located.

Diagram 5 accurately illustrates the converging, crossing, and diverging path of the light rays as they travel through the rectangular block.

The final answer is $\text{5}$.