Get last added item using rest

site/_vti_bin/listdata.svc/ListName?$select=Id&$orderby=Id%20desc&$top=1

Modal popup using xslt

  <a class="clsTitle" onclick="javascript:SP.UI.ModalDialog.ShowPopupDialog('{$SafeLinkUrl}'); return false;" title="{@LinkToolTip}">
                  <xsl:if test="$ItemsHaveStreams = 'True'">





<!--code for modal popup -->
  <xsl:template name="ModalDialogPopUp" match="Row[@Style='ModalDialogPopUp']" mode="itemstyle">
        <xsl:variable name="SafeLinkUrl">
            <xsl:call-template name="OuterTemplate.GetSafeLink">
                <xsl:with-param name="UrlColumnName" select="'LinkUrl'"/>
            </xsl:call-template>
        </xsl:variable>
        <xsl:variable name="DisplayTitle">
            <xsl:call-template name="OuterTemplate.GetTitle">
                <xsl:with-param name="Title" select="@Title"/>
                <xsl:with-param name="UrlColumnName" select="'LinkUrl'"/>
            </xsl:call-template>
        </xsl:variable>
        <div class="item link-item bullet">
            <xsl:call-template name="OuterTemplate.CallPresenceStatusIconTemplate"/>
            <a onclick="javascript:SP.UI.ModalDialog.ShowPopupDialog('{$SafeLinkUrl}'); return false;" onmouseover="javascript:this.style.cursor='hand';" title="{@LinkToolTip}">
                        <xsl:value-of select="$DisplayTitle"/>
            </a>
        </div>
    </xsl:template>
 
  <!-- End of modal popup code -->