Step 1: Think of the big figure as a grid of repeated tiles.
The wide black and white figure at the top is made by placing one small square tile again and again in rows and columns. Candidates P, Q, R and S are four possible versions of that tile.
Step 2: Use an overlay check.
Imagine placing each candidate tile directly on top of one block of the large figure, square by square. A true match means every black square in the candidate lines up with a black square in the figure, and every white square lines up with a white square.
Step 3: Test tile P.
When P is overlaid, at least one of its squares does not agree with the corresponding square in the large figure, so P fails the overlay check.
Step 4: Test tiles R and S.
The same overlay check on R and S also turns up a mismatched square in each case, a black square where the big figure has white, or the reverse. Both R and S are ruled out.
Step 5: Test tile Q.
When Q is overlaid on the reference block, every filled square and every empty square lines up exactly with the large figure. No mismatch remains anywhere in the tile.
Step 6: Conclude.
Since Q is the only candidate that survives the overlay check, it is the tile used to build the figure.
\[ \boxed{\text{Q}} \]
