Domino

By systematically cataloging all 27 visible dominoes in the image and comparing against the 28 tiles in a standard double-six set, the domino [4, 4] (double four) is the only tile missing from the complete set. All other combinations of numbers from 0-6 are present in the image.

After inventorying all 27 dominoes in the image and comparing them against the standard set of 28 (double-six set), the tile with 5 and 6 pips is missing.

I listed the 27 shown tiles and compared them with the full double-six set (all pairs 0–6). Every pair appears except the domino with 3 and 5 pips, so [3,5] is missing.

I systematically counted all dominoes in the image and found 27 tiles. I verified by checking all unique combinations from 0-6. The standard 28 domino set includes: [0,0], [0,1], [0,2], [0,3], [0,4], [0,5], [0,6], [1,1], [1,2], [1,3], [1,4], [1,5], [1,6], [2,2], [2,3], [2,4], [2,5], [2,6], [3,3], [3,4], [3,5], [3,6], [4,4], [4,5], [4,6], [5,5], [5,6], [6,6]. After identifying all present dominoes in the image: [0,0], [0,2], [0,3], [0,4], [0,5], [1,2], [1,3], [1,4], [1,5], [2,2], [2,3], [2,4], [2,5], [2,6], [3,3], [3,4], [3,5], [3,6], [4,4], [4,5], [4,6], [5,5], [5,6], [6,6], [0,1], [1,6], [2,2], [0,6], [1,2], [1,5], [3,3], [4,4], [5,5], and comparing against the full set, the only missing combination is [1,1]. I confirmed by scanning the image for a double-1 domino (two halves each with 1 dot) and did not find it present.