Radio buttons

<%= nk_radio_button "name", "value" %>

Radio group

Choose your fate

Coke

Coke Zero

<%= nk_radio_group :taste, value: :zero do |g| %>
  <%= g.title "Choose your poison" %>
  <%= g.item :coke, "Coke" %>
  <%= g.item :zero, "Coke Zero" %>
<% end %>