Sodium!

Girl student: That boy is sodium.
Me: Sodium?
Girl student: Yes, he is Mr. Sodium.
Me: …why?
Girl student: He is very reactive. He is always with the girls, you will always see him with many girls around him.

And then one of the boys, I forget whether it was Mr. Sodium or one of his friends, responded that, well, she could always be found with the boys around her.