OnCollisionEnter2D isn't working and I don't know why please help

I’m new to Unity and c# and I’m trying to get the basics down but I seem to be having some trouble with the collision. I want to get a falling object to destroy when it collides with another object that is stationary. All of the objects are set to Box Collider 2D in Unity and after hours of searching I can’t seem to figure out what’s wrong with it. Any help would be much appreciated!

if you script Destroy its attached to the gameobject that has to be destroyed simply put this OnCollisionEnter2D:

 void OnCollisionEnter2D(Collision2D col)
        {
                if (col.gameObject.tag == "Target") //|| (col.gameObject.tag == "fallingCube2"))
                {
                        Debug.Log ("There has been a collision!");
                        Destroy (gameObject);
                }
                if (col.gameObject.tag == "otherTarget")
                {
                        Debug.Log ("There has been a collision!");
                        Destroy (gameObject);
                }
}