How to get random int values to a prefab which is called multiple times(without repeating same value)?

I have created a prefab which contains text (a*b=) and input field (to get user's answer). and I am calling this prefab 5 times using c# script. I have assigned a & b to random.range(1,10) so i can get 5 different sums. but in my case i am getting same values to all 5 sums.

I tried foreach loop and it is getting random numbers out of given range and on clicking check button it shows even correct answers in red(as incorrect). This is the first time i am dealing with calling prefab multiple times via script. so need some help to solve it please.

TestModeQuestionUI.cs

using Helper.Keyboard;
using System;
using System.Collections;
using System.Collections.Generic;
using TMPro;
using UnityEngine;
using UnityEngine.UI;

public class TestModeQuestionUI : MonoBehaviour
{
internal RectTransform refRectTransform;
[SerializeField]
TextMeshProUGUI valueA; // valueB;
[SerializeField]
MyInputField AnswerInputField;
internal int id;
internal Action<TestModeQuestionUI> onSubmitValueOfInputFieldAction;
internal Action<TestModeQuestionUI> onSelectInputFieldAction;

Color defaultColorOfAnswer = new Color(0.19f, 0.19f, 0.19f, 1f);
Color correctColorOfAnswer = new Color(0f, 0.44f, 0f, 1f);
Color incorrectColorOfAnswer = new Color(1f, 0f, 0f, 1f);

public static TestModeQuestionUI curSelectedAnswerInputField;

//-------------------------------------------------------------------------

void Awake()
{
    refRectTransform = GetComponent<RectTransform>();
}


private void SetNextAnswerInputFieldAsSelected(TestModeQuestionUI 
curSelectedAnswerInputField)
{
    throw new NotImplementedException();
}

public void SetQuestionLabel(string v)
{
    valueA.text = v;        
}

public void ActiveAnswerInputField(bool active)
{
    AnswerInputField.gameObject.SetActive(active);
}

public int GetAnswerInputField()
{
    int result = -1;
    int.TryParse(AnswerInputField.textComponent.text, out result);
    return result;
}

public void SetAnswerInputField(string msg)
{
    AnswerInputField.textComponent.text = msg;
}

public void SelectAnswerInputField()
{
    DeSelectCurSelectedAnswerInputField();
    AnswerInputField.ActivateInputField();
    curSelectedAnswerInputField = this;   
}

public static void DeSelectCurSelectedAnswerInputField()
{
    if (curSelectedAnswerInputField != null)
    {            
       curSelectedAnswerInputField.AnswerInputField.DeactivateInputField();   
    }
       curSelectedAnswerInputField = null;
}

public void SetResultOfAnswerInputField(int result)
{
    switch (result)
    {
        //==================================
        // Default Color For Answer Has Not Checked
        case 0:
            AnswerInputField.textComponent.color = defaultColorOfAnswer;
            break;

        //==================================
        // Correct Color For Answer Has Checked Correct
        case 1:
            AnswerInputField.textComponent.color = correctColorOfAnswer;
            break;

        //==================================
        // Incorrect Color For Answer Has Checked Incorrect
        case 2:
            AnswerInputField.textComponent.color = incorrectColorOfAnswer;
            break;
    }
}

public void OnSelectInputField()
{
    //Debug.Log("On Select : " + id);
    if (curSelectedAnswerInputField != this)
        DeSelectCurSelectedAnswerInputField();
    curSelectedAnswerInputField = this;

    if (onSelectInputFieldAction != null)
        onSelectInputFieldAction(this);
}

public void OnSubmitValueOfInputField()
{
    if (onSubmitValueOfInputFieldAction != null)
        onSubmitValueOfInputFieldAction(this);
}

}

TestModeManager.cs

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

 public class TestModeManager : MonoBehaviour
 {
 public static TestModeManager instance;
 [SerializeField]
 GameObject refTestModeQuestionExampleParent;
 [SerializeField]
 GameObject refTestModeQuestionExamplePrefab;
 [SerializeField]
 GameObject checkButton;
 [SerializeField]
 GameObject nextButton;

 private int a, b;
 List<TestModeQuestionUI> testModeQuestionExampleList;


 void Start()
 {
    CreateUI();
 }

 void Update()
 {        
 #if UNITY_EDITOR
    if (Input.GetKeyDown(KeyCode.KeypadEnter))
    {    SetNextAnswerInputFieldAsSelected(TestModeQuestionUI.curSelectedAnswerInputField);          



    }
 #endif

    if (Input.GetKeyDown(KeyCode.Escape))
    {
        if (Keyboard.instance.gameObject.activeInHierarchy)
            Keyboard.Close();
        else
            Application.Quit();
    }
 }


 void CreateUI()
 {
    GameObject _GO;
    TestModeQuestionUI _TestModeQuestionUIRefrence;

    if (testModeQuestionExampleList == null)
        testModeQuestionExampleList = new List<TestModeQuestionUI>();

   //  a = UnityEngine.Random.Range(1, 20);
  //   b = UnityEngine.Random.Range(1, 10);

    for (int id = 1; id <= 5; id++)
    {
        _GO = Instantiate(refTestModeQuestionExamplePrefab, 
 refTestModeQuestionExampleParent.transform);
        _GO.name = "TestModeQuestion Example " + id;
        _TestModeQuestionUIRefrence = _GO.GetComponent<TestModeQuestionUI> 
 ();
        _TestModeQuestionUIRefrence.id = id;
        _TestModeQuestionUIRefrence.onSubmitValueOfInputFieldAction = 
  SetNextAnswerInputFieldAsSelected;
        testModeQuestionExampleList.Add(_TestModeQuestionUIRefrence);

  }

    ResetUI();               
  }

  void ResetUI()
  {
    // Reset Multiplication Examples
    a = UnityEngine.Random.Range(1, 10);
    b = UnityEngine.Random.Range(1, 10);
    foreach (TestModeQuestionUI _TestModeQuestionUIRefrence in 
  testModeQuestionExampleList)
    {
        _TestModeQuestionUIRefrence.SetQuestionLabel(a + "            " +  
  b + "  = ");

   //loop to get 5 different sums
   var questions = GameObject.FindGameObjectsWithTag("question");
   foreach (var question in questions)
   {
         // a++;
         //b++;
  }

   }
  //==================================
    // Set First Answer Input Field As Selected
    SetNextAnswerInputFieldAsSelected();

  }
  void SetNextAnswerInputFieldAsSelected(TestModeQuestionUI _ 
  TestModeQuestionUIRefrence = null)
  {
    if (_TestModeQuestionUIRefrence == null)
    {
        //==================================
        // Get First Input Field And Set As Selected
        _TestModeQuestionUIRefrence = GettestModeQuestionExampleList(1);
        if (_TestModeQuestionUIRefrence != null)
            _TestModeQuestionUIRefrence.SelectAnswerInputField();
    }
    else
    {
        //==================================
        // Get Next Input Field And Set As Selected
        _TestModeQuestionUIRefrence = 
  GettestModeQuestionExampleList(_TestModeQuestionUIRefrence.id + 1);
        if (_TestModeQuestionUIRefrence != null)
            _TestModeQuestionUIRefrence.SelectAnswerInputField();
        else
        {
            Keyboard.Close();
            StartCoroutine(highlighCheckButton());
        }
    }
  }

  TestModeQuestionUI GettestModeQuestionExampleList(int id)
  {
    foreach (TestModeQuestionUI _TestModeQuestionUIRefrence in 
  testModeQuestionExampleList)
    {
        if (_TestModeQuestionUIRefrence.id == id)
        {
            return _TestModeQuestionUIRefrence;
        }
    }
    return null;
  }
  IEnumerator EnableKeyboardAfterSometime(float time)
  {
    yield return new WaitForSeconds(time);
    Keyboard.Open();
  }

IEnumerator highlighCheckButton()
{
    checkButton.transform.localScale = new Vector3(1f, 1f, 1f);
    float animtionTime = 0.3f;
    float scaleUpTo = 1.2f;
    for (int i = 0; i < 4; i++)
    {
        yield return AnimationController.animate(scaleCheckButton, 
animtionTime, 1f, scaleUpTo);
        yield return AnimationController.animate(scaleCheckButton, 
animtionTime, scaleUpTo, 1f);
    }
    checkButton.transform.localScale = new Vector3(1f, 1f, 1f);
}

void scaleCheckButton(float value)
{
   checkButton.transform.localScale = new Vector3(value, value, value);
}

public void CheckButton()
{
    int answer;
    foreach (TestModeQuestionUI _TestModeQuestionUIRefrence in 
testModeQuestionExampleList)
    {
        answer = _TestModeQuestionUIRefrence.GetAnswerInputField();
        if ((a * b) == answer)
        {
            _TestModeQuestionUIRefrence.SetResultOfAnswerInputField(1);
        }
        else
        {
            _TestModeQuestionUIRefrence.SetResultOfAnswerInputField(2);
        }
    }

    checkButton.SetActive(false);
    nextButton.SetActive(true);
}

public void NextButton()
{
    ResetUI();
    nextButton.SetActive(false);

}