When two balanced dice are rolled, the sum of the dice can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, giving 11 possibilities. therefore the probability is 1/11 that the sum is 12?

False.

There are 36 possible outcomes, corresponding to numbers 1-6 independently appearing on each of the dice. Only one of those outcomes is double-sixes, resulting in a sum of 12. The probability that the sum is 12 is 1/36.

In short, the 11 outcomes listed in your problem statement are not equally-likely.