Making a time bomb

I want to spawn multiple bombs in random locations, and give them 5 seconds before detonation. Yet, all the clones switch their tags back to "unt" without changing to "explosion" after 5 seconds, except the first original bomb.

Here is my code:

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class sc : MonoBehaviour {

 public Sprite bomb;
 public Sprite explo;
 public GameObject player;
 public GameObject bx;
 

 public float timer;


  


 // Start is called before the first frame update
 void Start ()

 {


    // this.gameObject.GetComponent<SpriteRenderer>().sprite = bomb;
     timer = 0;
 }

 // Update is called once per frame
 void Update()
 {

     timer += Time.deltaTime;

   

     if (timer >= 5)
     {

         if (this.gameObject.GetComponent<SpriteRenderer>().sprite == bomb)
         {

             this.gameObject.GetComponent<SpriteRenderer>().sprite = explo;
             this.gameObject.tag = "explosion";

            
         }

         if (timer >= 6)
         {
             bx.transform.position = new Vector3(10, 0, 0);
             this.gameObject.tag = "unt";

             timer = 0;
             return;
         }
     }
    

 }

 private void OnTriggerStay2D(Collider2D collision)
 {
     Debug.Log("trigger");

     if(bx.tag == "explosion")
     {


         Destroy(player);

     }
     

 }

}

And here is the code for the spawner:

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class spwnrrr : MonoBehaviour {

 public GameObject bombPrefab;
 public float timer;
 public float posx;
 public float posy;  




 // Start is called before the first frame update
 void Start()
 {


     timer = 0;

     


 }

 // Update is called once per frame

   

 void Update()
 {
     timer += Time.deltaTime;

   

     if (timer >= 5)
     {

         transform.position = new Vector3(Random.Range(-4, 4), Random.Range(-4, 4), 0);

         posx = transform.position.x;
         posy = transform.position.y;


         Instantiate(bombPrefab, transform.position = new Vector3(posx, posy, 0), Quaternion.identity);





         timer = 0;
     }


 }

}