Now am using the code like this, i.e.. Using List with controller. But still facing the error . and please check the below code and check modifications and is anyone aware of the error then please post the solution for the same.

|Insert failed. First exception on row 0; first error: REQUIRED_FIELD_MISSING, Required fields are missing: [Candidate_Name__c, Father_Name__c]:

/*This apex class is used to save the Entrance Registration Data Entrance Registration Object, and Educational Information
of student. And educational information data is saving in Educational Information object.*/

//Apex Class
public class EntranceRegistrationCls{
 
    //Variable Declaration
    public String MasterId = '';
    public String EduRecordID;
    String TabURL;
    
    //Getter Setter Property Declaration
    public List<Educational_Information__c> EduList{get; set;}
    public List<Entrance_Registration__c> EntList{get; set;}   
    public Educational_Information__c Education{get;set;}
    
    //List Delcaration
    public list<Educational_Information__c> delList = new list<Educational_Information__c>();   
    public Entrance_Registration__c EntranceReg = new Entrance_Registration__c();
    public Entrance_Registration__c CurrentEntranceReg ;     
    ApexPages.StandardController controller;
    
    //constructor of EntranceRegistrationCls class
    public EntranceRegistrationCls(ApexPages.StandardController controller){        
        try{
            system.debug('yess');
            this.controller = controller;
            EntList = new List<Entrance_Registration__c>();
            EntList.add(new Entrance_Registration__c());
            EduList= new List<Educational_Information__c>();        
            EduList.add(new Educational_Information__c());
            Education= new Educational_Information__c();
            getMasterId();            
                if(MasterId == null || MasterId == ''){
                }else{
                    system.debug('Truee..>>'+MasterId);     
                    EntranceReg =[SELECT Id,Name FROM Entrance_Registration__c WHERE Id =:MasterId];
                    EduList=  [SELECT Id,Board_University__c,Degree_Diploma_Certificate_Etc_specify__c, Year_of_Passing__c,Education__c,Institute_College__c,Marks_CGPA__c,Mode_of_Education__c,
                               Status__c FROM Educational_Information__c WHERE Entrance_Master_Id__c =: EntranceReg.Id ];
                    system.debug('Yesssss--->>'+EduList);
                } 
        }
        catch(Exception ex){  
            ApexPages.Message myMsg = new ApexPages.Message(ApexPages.Severity.ERROR, ex.getMessage());
            ApexPages.addMessage(myMsg);
        }
    }
    //End of Constructor
    
    //Get Method for getting the current page id of Entrance Registration    
    public String getMasterId() {
        if(MasterId == null || MasterId == '')
            MasterId= ApexPages.CurrentPage().getParameters().get('ID');
            return MasterId;
    }
    //End of Get Method
    
    //Set Method for setting the value of Enratnce Registration    
    public void setMasterId(String val){
        MasterId = val;
    }
    //End of Set Method
    
    //To add any row method  
    public void addrow() {                              
        for(Integer i=0;i<EduList.size();i++){           
            EduList.add(new Educational_Information__c());                 
            return;
        }
    }
    //To remove any row method        
    public void removeRow(){  
        Integer i = EduList.size();
        if(EduList[i-1].Id <> null)
        delList.add(EduList[i-1]);
        EduList.remove(i-1); 
    }  
    // Save method to save whole data
    public PageReference save(){        
        Schema.DescribeSObjectResult SObjectResult = Schema.SObjectType.Entrance_Registration__c;
        String ObjectKey = SObjectResult.getKeyPrefix();
        TabURL = '/'+ ObjectKey +'/o';
        system.debug('Yes....>>'+TabURL);
            try{
                EntranceReg = (Entrance_Registration__c)controller.getRecord();
                CurrentEntranceReg = EntranceReg;
                system.debug('Yuuuupp>>>>'+CurrentEntranceReg);
                        
            }
            catch (Exception ex){
                ApexPages.Message errMsg = new ApexPages.Message(ApexPages.Severity.ERROR, ex.getMessage());
                ApexPages.addMessage(errMsg);
                return null;
            }
            try{
                if(CurrentEntranceReg.id <> null){
                        update CurrentEntranceReg;
                } else{
                        insert CurrentEntranceReg;
                  }
                  system.debug('Yes'+EduList);
                  EntList.add(CurrentEntranceReg);
                  system.debug('^^^^^^^List^^^^^^^'+EntList);
                for(Educational_Information__c ast: EduList){
                    if(ast.Id == null) 
                        ast.Entrance_Master_Id__c =  CurrentEntranceReg.ID;                        
                        ast.Education__c = ast.Education__c;
                        system.debug('Trueeeee...>'+ast.Entrance_Master_Id__c);
                        ast.Board_University__c = ast.Board_University__c;
                        ast.Institute_College__c = ast.Institute_College__c;
                        ast.Marks_CGPA__c = ast.Marks_CGPA__c;
                        ast.Mode_of_Education__c = ast.Mode_of_Education__c;
                        ast.Status__c = ast.Status__c;
                        ast.Year_of_Passing__c = ast.Year_of_Passing__c;
                        ast.Degree_Diploma_Certificate_Etc_specify__c=ast.Degree_Diploma_Certificate_Etc_specify__c;                    
                 }
                 system.debug('TRUE--->'+EduList);   
                upsert EduList;          
            }
            catch (Exception ex){
                ApexPages.Message errMsg = new ApexPages.Message(ApexPages.Severity.ERROR, ex.getMessage());
                ApexPages.addMessage(errMsg);
                return null;
            }            
            PageReference home = new PageReference(TabURL);        
            home.setRedirect(true);        
            return home;                                                
    }
    //End of Save Method
    static testMethod void testEntranceReg(){
        
        Test.startTest();
        /*Entrance_Registration__c[] EntReg = new Entrance_Registration__c[]{
            new Entrance_Registration__c(
                Candidate_Name__c='Neeru Nagpal',Father_Name__c='Mr. Rakesh Nagpal')};
         insert EntReg;
         
        pagereference pg=new pagereference('/apex/EntanceRegistrationVf'); 
        system.test.setCurrentpage(pg); 
        //object Entrance_Registration__c=new object();
        ApexPages.StandardController sc = new ApexPages.StandardController(new Entrance_Registration__c());
        EntranceRegistrationCls cn = new EntranceRegistrationCls(sc);
        //cn.property1 = pg.getparameters().get('id');
        cn.addrow();
        cn.removeRow();
        cn.save();*/

        PageReference PageRef = Page.EntranceRegistrationVf;
        test.setCurrentPage(PageRef);
        
       ApexPages.StandardController thecontroller = new ApexPages.StandardController(new Entrance_Registration__c());
       EntranceRegistrationCls controller = new EntranceRegistrationCls(thecontroller);
       controller.addrow();
       controller.removeRow();
       String MasterId;
       controller.setMasterId(MasterId);
 
        for(Entrance_Registration__c Ent:controller.EntList){
            Ent.Candidate_Name__c ='Test Name';
            Ent.Father_Name__c ='Test Father Name';
        }
        controller.save();
        Test.stopTest();    
    }              
   
   /* static testMethod void myUnitTest() {
        PageReference PageRef = Page.EntranceRegistrationVf;
        test.setCurrentPage(PageRef); 
        Apexpages.Standardcontroller sc = new Apexpages.Standardcontroller(new Entrance_Registration__c());
        EntranceRegistrationCls controller = new EntranceRegistrationCls(sc);
        String MasterId;
        controller.setMasterId(MasterId);
        controller.addrow();
        controller.removeRow();
        controller.save();
    }*/
 
}
//End of Apex Class