Range length or last element
{{ $list := (where .Site.Pages "Section" "blablabla") }}
{{ $len := (len $list) }}
{{ range $index, $element := $list }}
{{ if eq (add $index 1) $len }} do something {{ end }}
{{ end }}
<!-- Example from my Hugo Template: -->
{{ $list := (.Site.Menus.main) }}
{{ $len := (len $list) }}
{{ range $index, $element := $list }}
<li class="dib lh-copy"><a{{ if eq (add $index 1) $len }} class="ph2"{{ else }} class="br ph2"{{ end }} href="{{ .URL | absURL }}">{{ .Pre }} {{ .Name }}</a></li>
{{ end }}