Domino

The excluded domino is number 2 and 2

After cataloging all 27 dominoes shown in the image, all pairs from [0,0] to [6,6] are present except for the double-four ([4, 4]) tile.

By systematically checking all 28 possible dominoes in a standard double-six set, I can identify which domino is present in the image. After carefully examining each domino shown, all dominoes are present except [4, 4]. The double-four (four dots on both sides) is the missing tile from this set of 27 dominoes.

I identified each visible domino and found every pair from 0–6 except the tile with 2 and 4; the (2,4) domino does not appear among the 27 shown.

By systematically identifying all dominoes in the standard double-six set (28 total) and marking those visible in the image (27 present), the missing domino is [5,5]. All other doubles are accounted for: [0,0] in row 4, [1,1] in row 6, [2,2] in row 2, [3,3] in row 2, [4,4] in row 1, and [6,6] in row 6. The domino [0,6] appears as a vertical tile in row 4, and [5,6] appears in row 1, leaving [5,5] as the only missing tile from the complete set.