Step 1: Understand what the question is asking.
The large figure at the top is built by repeating one small tile pattern across a grid. Four candidate tiles, P, Q, R and S, are shown, and only one of them is the actual repeating unit used to build the big figure.
Step 2: Pick a reference block from the large figure.
Look closely at one block-sized region of the large figure, matching the size of the candidate tiles. Note exactly which small squares inside that block are filled black and which are white, along with their positions relative to the block's corners.
Step 3: Compare this reference block against each candidate tile.
Check each candidate for an exact match in the black-and-white square layout, keeping the same orientation as the repeating grid. A single extra or missing black square, or a shifted step in the zigzag shape, rules a candidate out.
Step 4: Eliminate the tiles that do not match.
Tiles P, R and S each differ from the reference block in at least one square, a black square appears where the large figure shows white, or the other way round, when placed in the same orientation as the repeating grid.
Step 5: Confirm the matching tile.
Tile Q reproduces the same black-and-white square layout, in the same orientation, as every repeated block inside the large figure.
Step 6: Final Answer.
\[ \boxed{\text{Q}} \]
The pattern labelled Q is used to generate the given figure, so the correct option is (B).
