regarding check box

Try Mutually Exclusive CheckBox ajax control
http://www.asp.net/ajaxLibrary/AjaxControlToolkitSampleSite/MutuallyExclusiveCheckBox/MutuallyExclusiveCheckBox.aspx[^]

You have to use javascript for doing this.

In the javascript code, you will write code to handle the click event and deselect all other checkbox.

If you are using jQuery, then you can write:

$('#container').find('input:checkbox').each(function() {
    $(this).click(function() {
        if($(this).is(':checked')) { // If it is checked, then uncheck all other checkbox.
            $('#container').find('input:checkbox').not($(this)).attr('checked', false);
        }
    });
});

<div id="container">
    <label><input type="checkbox" value="0" />Apple</label>
    <label><input type="checkbox" value="1" />Banana</label>
    <label><input type="checkbox" value="2" />Pineapple
</div>

if (chk1.Checked == true)
{
   chk2.Enabled = false;
}
else
{
    chk2.Enabled = true;
}