Domino

The excluded domino is number 0 and 6

By systematically counting all dominoes in the double-six set, I found that out of the 28 unique tiles, only 27 are present in the image. The missing tile is the [0, 6] (blank and six) domino.

By systematically cataloging all 27 visible dominoes and comparing against the complete set of 28 possible dominoes (all unique pairs from 0-6), the domino [0, 1] is the only one missing from the standard double-six set.

I inspected each domino in the image and tallied the pairs; every combination from the double-six set appears except the 4–5 tile, so the missing domino is [4,5].

After carefully examining the arrangement of the 27 dominoes in the provided image and comparing against the complete double-six set of 28 dominoes, the [2|6] tile is the one absent.

I systematically identified the dominoes in the image. A standard double-six set contains 7 doubles: [0,0], [1,1], [2,2], [3,3], [4,4], [5,5], and [6,6]. In the image, I can clearly identify six of these doubles: [0,0] (vertical blank domino in the fourth row), [1,1] (horizontal in the fourth row), [2,2] (horizontal in the second row), [3,3] (horizontal in the third row), [4,4] (horizontal in the fourth row left), and [5,5] (vertical in the top row). The only double missing is [6,6], which would show 6 dots on both halves (arranged as two columns of three dots each). This domino is not present in the image.