Свойство зависимости WPF MVVM

 Try with the below codes. All should work. 
    $('select').val(2);
    $('select').prop('selectedIndex', 1);
    $('select>option[value="5"]').prop('selected', true);
    $('select>option:eq(3)').attr('selected', 'selected');
    $("select option:contains(COMMERCIAL)").attr('selected', true);