NEED HELP!!! How to explode my enemy ship? Need help with C# script

The idea is to throw a bomb and if it touches the Sphere collider in which my enemy ship is placed, it must destroy the enemy ship. So, first of all I must say that I'm new in C#, and with all that I know I tried to write a script to do so. I haven't got any errors, though it does't work. I'm sure it's some logical mistake in the script and I would appreciate a lot if someone helped me with it. I need it for a project, and I've got a deadline.....

so here goes the sript that I attached to the bomb:

 float lifespan = 3.0f;
 public GameObject explosionEffect;
 public GameObject enemy;
 
 void Update () {
     lifespan -= Time.deltaTime;
     if(lifespan <= 0)
     {
         Explode();
     }
 }
 void OnCollisionEnter(Collision collision)
 {
     if (collision.gameObject.tag == "Enemy")
     {
         Explode();
         Destroy(enemy);
         Instantiate(explosionEffect, transform.position, Quaternion.identity);
     }
 }
 void Explode()
 {
     Destroy(gameObject); 
 }

And I also tried to attach a 'Explode" script to the enemy ship, yet it doesn't work either...: void Update () {

 }
 void OnCollisionEnter(Collision collision)
 {
     if (collision.gameObject.tag == "Granade")
     {
         Destroy(gameObject);
         //Instantiate(explosionEffect, transform.position, Quaternion.identity);
     }
 }

Note that the bomb has got the tag "Granade" and the enemy ship has got the tag "Enemy". Thanks a lot!