For simplicity, let 1H be a, 2H be b, 3H be c, 16O be d, 17O be e, and e, 18O be F. 。
A water molecule consists of two hydrogen atoms 1 oxygen atoms. That is to say, you have to choose two from ABC and one from DEF, which makes three altogether. ..
There are six kinds of hydrogen atoms, namely AA, BB, CC, AB, AC and BC.
Then for each choice, it can correspond to the choice of three kinds of oxygen atoms, namely DEF:
Ade, AAE, AAF
BBD、BBE、BBF
………………
Wait ~
1H- 1H- 16O
1H- 1H- 17O
1H- 1H- 18O
1H-2H
1H-2H
1H-2H
1H-3H- 16O
1H-3H- 17O
1H-3H- 18O
2H-2H- 16O
2H-2H- 17O
2H-2H- 18O
2H-3H- 16O
2H-3H- 17O
2H-3H- 18O
3H-3H- 16O
3H-3H- 17O
3H-3H- 18O
Note: I am a sophomore. I'm not in senior three yet. In my senior year, I will focus on combinatorics. At that time, such a question would be very simple. You look like you just graduated from Grade Three or Grade One. Now we don't understand combinatorics, and even if someone lists it, we can't understand its meaning. So now such a problem can only be solved in this way.