Select a figure from the given four alternatives which fits exactly into…

In a figure-completion question, a square has been cut into two pieces by a single zigzag boundary line. A candidate piece completes the square with the given piece only if its own straight outer edges supply exactly the sides of the square that the given piece is missing, meeting at the one right-angle corner still needed, and its jagged inner boundary is the exact mirror match of the given piece's cut edge, so the two boundaries interlock without any gap or overlap.

Figure-X already contributes the complete top edge and the complete left edge of the square, meeting at its own top-left corner, so the matching piece must supply the missing bottom edge and right edge, meeting at the bottom-right corner. Tracing Figure-X's cut line, a two-step staircase followed by a sharp zigzag notch running from its lower point up to its upper point, the matching piece's cut must retrace this same staircase-and-zigzag path as its mirror image. Among the alternatives, Figure (2) is drawn with its own two straight edges at its left and bottom; turning Figure (2) so that these two edges take up the square's missing right and bottom sides, its staircase-and-zigzag notch then aligns exactly, step for step and point for point, with Figure-X's cut line, so it locks into Figure-X with no gap and no overlap.

• Figure (1) and Figure (4): each repeats Figure-X's own top-left corner and ends in an extra slanted edge instead of a clean right-angle corner, so a gap remains where a straight edge is needed.

• Figure (3): the general staircase-and-zigzag shape looks similar, but its steps are offset from Figure-X's actual cut line, so the two boundaries would not interlock cleanly.

Hence, Figure (2) is the piece that completes the square.