Handle mouse click on a gameobject - Unity3d

I have a small city mesh and an apartment 3d model. I add the mesh to my scene and place the 3d model on the mesh.

I try to handle mouse click only on 3d model. I use below code. But I click anywhere on the screen, it sets as sound = true

I add a mesh collider to 3d model gameobject.

if (Input.GetMouseButtonDown (0)) {
            Plane p = new Plane (Camera.main.transform.forward , transform.position);
            Ray r = Camera.main.ScreenPointToRay (Input.mousePosition);
            float d;
            if(p.Raycast (r, out d)) {
                sound = true;
}   

How can I solve it?

you can check tag/name of game object. you need to use like that:

void Update() 
{
    if (Input.GetMouseButtonDown (0)) {

        Plane p = new Plane (Camera.main.transform.forward , transform.position);
        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        RaycastHit hit;

        if (Physics.Raycast(ray, out hit, 100)) 
        {
            //Choose one of them below!!!

            /// Name Comparison
            if(hit.collider.gameObject.name.equals("NameOfTheObject")){
               ///Do Logic
            }

            //Tag Comparison
            if(hit.collider.gameObject.CompareTag("TagOfTheObject")){
                ///Do Logic
            }
        }
    }
}