Is yeast a grain?

No. Yeast is a plant cell,it does not form a seed.

Is there any other grains that can be spelled out of "Merry Christmas?"

I already know riceis a grain.

rye

Great job! You already know that "rice" is a grain that can be spelled out of "Merry Christmas." Another grain that can be spelled out of "Merry Christmas" is "rye."

To determine if a word can be spelled out of another word or phrase, you can simply look for the letters in the given word or phrase and see if they can form a valid word. In this case, we can find the letters "r," "y," and "e" in "Merry Christmas," which can be rearranged to spell "rye."