The best way to do this is by using ordered list
<ol></ol>
or unordered list
<ul></ul>
Place all your radio buttons in a li tag of an ul. like this.
<ul>
<li>
<asp:radiobutton id="Question1_Option1" text="" runat="server" groupname="GroupQuestion1" xmlns:asp="#unknown" />
</li>
<li>
<asp:radiobutton id="Question1_Option2" text="" runat="server" groupname="GroupQuestion1" xmlns:asp="#unknown" />
</li>
<li>
<asp:radiobutton id="Question1_Option3" text="" runat="server" groupname="GroupQuestion1" xmlns:asp="#unknown" />
</li>
</ul>