Domino

After systematically identifying all 27 dominoes visible in the image, I can confirm that the double-four [4, 4] is the missing tile from the standard 28-piece double-six domino set. All other 27 unique combinations have been accounted for.

The excluded domino is number 3 and 1

After cataloging all 27 dominoes in the image, the missing tile from the standard double-six set (28 tiles) is the [6, 4] domino. The tiles present are: [1,6], [2,4], [0,4], [1,4], [4,6], [1,3], [1,1], [0,2], [2,2], [0,3], [1,5], [6,6], [3,5], [0,6], [5,6], [1,2], [0,1], [2,5], [2,3], [0,5], [2,6], [0,0], [3,4], [3,3], [3,6], [5,5], [4,4].

I systematically catalogued all visible dominoes in the image and compared them against the full standard set of 28 dominoes (0-0 through 6-6). After identifying all 27 visible tiles, the domino [0,3] (blank-three) was the only combination not present in the image.

The excluded domino is number 2 and 5

After counting the occurrences of each number across all halves in the 27 dominoes, numbers 0,1,2,4,6 appear 8 times each, while 3 and 5 appear 7 times each, indicating the missing domino is [3,5].

After identifying all visible dominoes in the set, I found 27 dominoes present. The doubles present are [0,0], [1,1], [2,2], [3,3], [4,4], and [5,5]. The only double missing from the complete set is [6,6], which is the highest domino in a double-six set.