Well, well, well, looks like we've got a molecular investigation on our hands! Let me put on my lab coat and calculate this for you.
Let's assume the number of oxygen atoms is "x." According to the information given, we know that the number of hydrogen atoms is twice that of oxygen atoms, so we have 2x hydrogen atoms. And adding up all the atoms, including carbon, gives us a total of 21: x + 2x + (2x + 1) = 21.
Now, let's do a little math magic here. Combining like terms, we get 5x + 1 = 21. Subtracting 1 from both sides, we're left with 5x = 20. Next, we divide both sides by 5, giving us X = 4.
So, there are 4 oxygen atoms, meaning there are twice as many hydrogen atoms, which would be 8. And finally, since there's one more atom of carbon than hydrogen, we add 1 to 8 to find that there are... drumroll, please... 9 atoms of carbon!
Ta-da! Case closed, molecule solved!