Which spieces contains a coordinate covalent bond?

Question

*
A) * Hg x Hg x] 2+

B)
* ** *
H x N x H
*x
H

C) *
H x H

D)

* xx x
[ H x O x H ] +

x*
H

Note: The * is used as a little circle.

Answer 1

Don't try to draw Lewis diagrams on Yahoo. It just doesn't work!

But (H3O)+ contains a dative covalent bond...