Domino

The image contains 27 dominoes. A standard double-six domino set has 28 tiles. Upon examining the image, it is evident that the domino [6, 6] is missing.

After cataloging all 27 dominoes in the image and comparing them to a full double-six set, the [6, 6] tile is the only one missing.

By systematically identifying all visible dominoes in the image and comparing against the complete standard double-six set of 28 tiles, the domino [2, 4] (or [4, 2]) is the only tile that is not present among the 27 dominoes shown. All other combinations from [0, 0] through [6, 6] are accounted for.

By systematically cataloging all visible dominoes in the image and comparing them to a complete standard double-six set (28 tiles), I identified that the [1,4] domino is missing. All other combinations from [0,0] through [6,6] are present in the image.

I identified all 27 tiles shown in the image and the only missing pair from the full double-six set is the domino with 4 and 6.

A complete double-six domino set contains 28 dominoes. Examining the image, I can identify 27 dominoes present, including all doubles from [0|0] through [5|5]. The double [6|6] is the only double that does not appear in the grid. Specifically, I can see: [0|0], [1|1], [2|2], [3|3], [4|4], and [5|5] all present, but no domino with six dots on both sides. Therefore, [6|6] is the excluded domino.