void OnCollisionEnter2D(Collision2D col){

if (col.gameObject.tag == "Enemy") {

     score = score + 50;
     Destroy (gameObject);
    *Here I need to wait for 3 sec then it should load the next level*
     SceneManager.LoadScene(nextLevel);

void OnCollisionEnter2D(Collision2D col){

     Debug.Log ("Collision");


         if (col.gameObject.tag == "Enemy") {

             score = score + 50;
             Destroy (gameObject);

           StartCoroutine (WaitForIt (3.0F));

IEnumerator WaitForIt(float waitTime) {
 yield return new WaitForSeconds(waitTime);
 SceneManager.LoadScene(nextLevel);