if(((RadioButton) grp_options.getChildAt(grp_options.getCheckedRadioButtonId())).getText().equals(rightAnswers.get(i))) // Error at this expression
    {
        trueResult++;
    }

grp_options.findViewById(grp_options.getCheckedRadioButtonId())

if(((RadioButton) grp_options.getChildAt(grp_options.getCheckedRadioButtonId())).getText().equals(rightAnswers.get(i)))

if(((RadioButton) findViewById(grp_options.getCheckedRadioButtonId())).getText().toString().equals(rightAnswers.get(i)))

if(((RadioButton) grp_options.getChildAt(grp_options.getCheckedRadioButtonId())).getText().toString().equals(rightAnswers.get(i)))