dropdown menu

<tr>
				<td ><input type=checkbox /></td>
				<td>2</td>
					<td class='list_submenu' onclick="showhide_list_submenu('2')">workmates
							<ul class = 'list_submenu_dropdown' id='2'>
								<li>Edit</li>
								<li>Contacts</li>
								<li>Delete</li>
							</ul>
						</td>
			</tr><tr>
				<td ><input type=checkbox /></td>
				<td>3</td>
					<td class='list_submenu' onclick="showhide_list_submenu('4')">test2
							<ul class = 'list_submenu_dropdown' id='4'>
								<li>Edit</li>
								<li>Contacts</li>
								<li>Delete</li>
							</ul>
						</td>
			</tr><tr>
				<td ><input type=checkbox /></td>
				<td>4</td>
					<td class='list_submenu' onclick="showhide_list_submenu('5')">test3
							<ul class = 'list_submenu_dropdown' id='5'>
								<li>Edit</li>
								<li>Contacts</li>
								<li>Delete</li>
							</ul>
						</td>
			</tr>

//question
how can i show hide the item dropdown submenu every time a user clicks on an element