tag of the clicked object

I am making a Block’D game for practice. But I am running into some problems.
1- how do I check if the boxes next to each other are of same type or not. they could be more then one or two.

2- I am making it in 2D so will it be fine to make the boxes drop down to fill empty spaces or should I make it in 3D?

If there are any tutorials for the game they will be helpful. I tried making it in 2D but got stuck after setting up the board.

First create a new type of ID and assign it to your instances, then just compare ID:

void OnCollisionEnter(Collision collision) {
		collision.collider.GetInstanceID () == "yourID";