better to use touchstart event with .on() jQuery method:
$(window).load(function() { // better to use $(document).ready(function(){
$('.List li').on('click touchstart', function() {
$('.Div').slideDown('500');
});
});
And i don't understand why you are using $(window).load() method because it waits for everything on a page to be loaded, this tend to be slow, while you can use $(document).ready() method which does not wait for each element on the page to be loaded first.