Finishing up my 2D quiz game [Last Problem]

I have problem with my true false quiz game. I'm still new at using unity. Here is the link to my problem that I write on forum because its more clear and easy to understand there. https://forum.unity.com/threads/finishing-up-my-2d-quiz-game.1129834/

But here is the summary:

1. I try to make the game end and show congratulation screen IF the player answer 20 question correctly but the unity keep freezing when I answer the 19th question. Even if I make the index to 10 or 5 for example, it freeze in 9th or 4th question. So basically it always freeze on the last 2 question.

2. I try to make the game end and show game over screen IF the player answer 1 question wrong. And the game over screen will also tell the last score that player currently have. But the problem is I still don't know how to make it happen.

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Here is the scripts on my game that I think relevant to my game:

• Result Script : The core of the game. To manage in game button, score, transition for next question, etc

  ---

  using System.Collections; using System.Collections.Generic; using UnityEngine; using UnityEngine.UI; using UnityEngine.Events; using UnityEngine.SceneManagement;

  public class Result : MonoBehaviour { public Questions questions; public GameObject correctSprite; public GameObject incorrectSprite; public GameObject completeLevelUI;

     public GameOverScreen gameOverScreen;
   
       public Scores scores;
   
       public Button trueButton;
       public Button falseButton;
   
       public UnityEvent onNextQuestion;
   
       void Start()
       {
           correctSprite.SetActive(false);
           incorrectSprite.SetActive(false);
       }
   
       public void ShowResults(bool answer)
       {
           correctSprite.SetActive(questions.questionsList[questions.currentQuestion].isTrue == answer);
           incorrectSprite.SetActive(questions.questionsList[questions.currentQuestion].isTrue != answer);
   
           if (questions.questionsList[questions.currentQuestion].isTrue == answer)
               scores.AddScore();
           else
               scores.DeductScore();
   
           trueButton.interactable = false;
           falseButton.interactable = false;
   
           StartCoroutine(ShowResult());
       }
   
       private IEnumerator ShowResult()
       {
           yield return new WaitForSeconds(1.0f);
   
           correctSprite.SetActive(false);
           incorrectSprite.SetActive(false);
   
           trueButton.interactable = true;
           falseButton.interactable = true;
   
           onNextQuestion.Invoke();
       }
      
       public void CompleteLevel ()
       {
           completeLevelUI.SetActive(true);
       }
   }
  
  
  

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• Questions Script: To store question

  ---

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

  [CreateAssetMenu] [System.Serializable]

  public class Questions : ScriptableObject { [System.Serializable]

     public class QuestionData
       {
           public string question = string.Empty;
           public bool isTrue = false;
           public bool questioned = false;
       }
   
       public int currentQuestion = 0;
       public List<QuestionData> questionsList;
   
       public void AddQuestion()
       {
           questionsList.Add(new QuestionData());
       }
   }
  
  
  

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• QuestionsData Script : To manage question in game.

  ---

  using System.Collections; using System.Collections.Generic; using UnityEngine; using UnityEngine.UI; using UnityEngine.SceneManagement;

  public class QuestionsData : MonoBehaviour { public Questions questions; [SerializeField] private Text _questionText;

     void Start()
       {
           AskQuestion();
       }
   
       public void AskQuestion()
       {
           var randomIndex = 0;
           do
           {
               randomIndex = UnityEngine.Random.Range(0, 20);
           } 
           while (questions.questionsList[randomIndex].questioned == true);
   
           questions.currentQuestion = randomIndex;
           questions.questionsList[questions.currentQuestion].questioned = true;
           _questionText.text = questions.questionsList[questions.currentQuestion].question;
       }
   
       public void ClearQuestion()
       {
           foreach (var question in questions.questionsList)
           {
              question.questioned = false;
           }
       }
   }
   
  
  
  

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• Scores Script : For in game scoring

  ---

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

  public class Scores : MonoBehaviour { public Text scoreText; private int _currentScore;

     void Start()
       {
           _currentScore = 0;
           scoreText.text = _currentScore.ToString();
       }
   
       public void AddScore()
       {
           _currentScore += 10;
           scoreText.text = _currentScore.ToString();
       }
      
       public void DeductScore()
       {
           _currentScore = _currentScore > 0 ? _currentScore - 10 : 0;
       }
   }
   
  
  
  

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• Congratulation script : To create congratulation screen when the player answer 20 question correctly.

  ---

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

  public class Congratulation : MonoBehaviour { public Result result;

         void onTriggerEnter()
           {
               result.CompleteLevel();
           }
   }
   
  
  
  

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• GameOverScreen Script : To make the game over when the player answer the question wrong and show the current score.

  ---

  using System.Collections; using UnityEngine; using UnityEngine.UI;

  public class GameOverScreen : MonoBehaviour { public Text pointsText;

     public void Setup(int Scores)
       {
           gameObject.SetActive(true);
           pointsText.text = Scores.ToString();
       }
   }
   
  
  
  

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Please help. I'm still very new at this. This is actually the first game I ever made.