Domino

After cataloging all 27 dominoes shown in the image, the only tile missing from a standard double-six set (which contains 28 tiles) is the [6, 6] double-six tile.

The excluded domino is number 2 and 1

By systematically counting all visible dominoes in the image and cross-referencing against the 28 unique tiles in a standard double-six set, the domino [2, 4] is the only tile that is not present among the 27 dominoes shown.

Scanning the 27 visible tiles shows every combination of pips from 0–6 except the double-six tile; no tile with six pips on both halves appears, so the missing domino is [6,6].

In a standard double-six domino set, each number (0-6) appears exactly 8 times across all 28 tiles. By analyzing the 27 dominoes present in the image and counting occurrences of each number, the number 4 appears 7 times and the number 5 appears 7 times. All other numbers (0, 1, 2, 3, 6) appear 8 times. Since only one domino is missing, and both 4 and 5 appear one time fewer than expected (7 instead of 8), the missing domino must be the one containing both 4 and 5, which is [4,5].