Which number is spelled in alphabetical order?

To determine which number is spelled in alphabetical order, we analyze each of the options by looking at the initial letters of each word.

Starting with "Twelve," it is spelled as T-W-E-L-V-E. The letters are not in alphabetical order since W comes after L.

Next, "Forty" is spelled F-O-R-T-Y. Here, the letters are also not in alphabetical order since O (the second letter) comes after F (the first letter).

Then we have "Ten," spelled T-E-N. The letters do not form an alphabetical sequence either, as E comes before N, breaking the order.

Finally, we consider "Twenty," which is spelled T-W-E-N-T-Y. Looking at the letters: E comes before N, N comes before T, and T is followed by Y. Hence, when arranged, the sequence T, W, E, N, T, Y is found to be in the correct alphabetical order:

1. E

2. N

3. T

4. T

5. W

6. Y

Since "Twenty" is the only word where the letters can be arranged in a way that respects the alphabetical order without any interruptions between letters, it confirms that this is