Domino

The excluded domino is number 2 and 2

By counting all the domino tiles present in the image and cross-referencing them with a standard double-six set of 28 tiles, it’s possible to see that the [6, 0] tile (the blank-six tile) is missing.

Scanning the 27 shown tiles, every pair including doubles 0–0,1–1,2–2,3–3,4–4,5–5 is present while the double six (6–6) does not appear in the image, so the missing tile is [6,6].

The excluded domino is number 5 and 6

By analyzing the pips count: A standard double-six set has 28 dominoes with total pips = 168 (each number 0-6 appears exactly 8 times). Counting all visible pips in the 27 dominoes: Row 1: 26, Row 2: 22, Row 3: 22 (including [0,6] at position 4), Row 4: 30, Row 5: 27, Row 6: 32. Total = 159. Missing pips = 168 - 159 = 9. The dominoes with sum 9 are [3,6] and [4,5]. Since [4,5] is clearly present in row 4, position 4, the missing domino must be [3,6].

By counting the occurrences of each number (0-6) in the image, numbers 3 and 4 each appear 7 times (instead of the expected 8 in a full set). This indicates the missing domino is the one containing both 3 and 4.

By systematically checking all 28 possible dominoes in a standard double-six set, I identified 27 dominoes present in the image. The domino [2, 4] (or equivalently [4, 2]) is the only one missing from the complete set of all pairs from 0 to 6.