What Is This Plant's Name?

I were buying a small tank (21cm x14cm x17cm) 7 hours ago just in case in future I've got sick fishes, The shop keeper were cutting plants so she given me 2 along with the tank... Though one was having white spot on leaves so I throw that away, May I ask what this plant called? (So I can do research with a name given) The shop keeper told me just put it on water surface, they will just grow, I doubt though



side view


top view

Oh yes and is it okay just stick it into gravel? (Since it's from cut, there aren't any roots on it...)

Thanks

Looks like Egeria (a.k.a. Elodea Densa) to me. It's ok to put into the substrate yes, but I belive it's a floating plant.

Thanks for the information