Hide checkboxes in different situations of other backgrounds

I am creating this activity that a question is fetched from string-array using random. In different questions, I am giving a different background to my activity to match the question's topic. What I have is an on click listener for check boxes, where the user is needed to press on the correct check box for the selected question. I want to show different check boxes in different backgrounds (& questions) so I have implemented all the checkboxes in my layout including the android:visibility="gone" and trying to checkBox1.setVisibility(View.VISIBLE); I keep getting an NullPointerException in the line where I set the visibility of the checkbox to visible. Can somebody explain me that? code is below

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_tennis_facts);

    TextView countsTxt = (TextView) findViewById(R.id.txtCounts);
    questions = getResources().getStringArray(R.array.questions);       
    CheckBox centerBack = (CheckBox) findViewById(R.id.centerBack);
    CheckBox checkBox1 = (CheckBox) findViewById(R.id.checkBox1);
    CheckBox checkBox2 = (CheckBox) findViewById(R.id.checkBox2);
    CheckBox checkBox3 = (CheckBox) findViewById(R.id.checkBox3);
    CheckBox checkBox4 = (CheckBox) findViewById(R.id.checkBox4);
    CheckBox checkBox5 = (CheckBox) findViewById(R.id.checkBox5);
    CheckBox checkBox6 = (CheckBox) findViewById(R.id.checkBox6);

    centerBack.setOnClickListener(this);
    checkBox1.setOnClickListener(this);
    checkBox2.setOnClickListener(this);
    checkBox3.setOnClickListener(this);
    checkBox4.setOnClickListener(this);
    checkBox5.setOnClickListener(this);
    checkBox6.setOnClickListener(this);

    countsTxt.setTextColor(Color.parseColor("#0033CC"));
    countsTxt.setTextSize(24);
    countsTxt.setText("Tries: " + triesLeft); 

}

 @Override
    protected void onResume() {
        super.onResume();

        counts = 0;
        getQuestion();
    }

@SuppressLint("NewApi") private void getQuestion(){
    TextView questionText = (TextView) findViewById(R.id.question);
    questionText.setGravity(Gravity.CENTER_VERTICAL | Gravity.CENTER_HORIZONTAL);
    questionText.setTextSize(24);

    RelativeLayout screenGame = (RelativeLayout) findViewById(R.id.screenGame); 

    Random rand = new Random();
    int maxIndex = questions.length;
    int generatedIndex = rand.nextInt(maxIndex);        
    if(questions[generatedIndex].equals("Click on the player with the possition of a Center Back")){
        screenGame.setBackground(getResources().getDrawable(R.drawable.footballfindtheposition));
        checkBox1.setVisibility(View.VISIBLE);
    }
    else if(questions[generatedIndex].equals("Click on the area where Player should serve in order to be valid")){
        screenGame.setBackground(getResources().getDrawable(R.drawable.tenniscourt));
    }
    questionText.setText(questions[generatedIndex]);
}