_form.html.erb

<%= form_for(@post) do |f| %>
  <% if @post.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:</h2>

      <ul>
      <% @post.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>


	<script>

		$(document).ready(function() {
		 $('select#option').select2();
		});
	
	</script>


  <br><br>
  <div class="field">
    <%= f.label :name %><br>
    <%= f.text_field :name %>
    <%= select_tag(:option, 
    	options_for_select([['All', 1], ['Co', 2], ['Bought', 3], ['View', 4], ['Top API', 5]] )) %>
  </div>
  
  
  
  <div class="actions">
    <%= f.submit :class => "btn btn-primary" %>
  </div>
<% end %>

application.css

 *= require bootstrap
 *= require_tree .
 *= require_self
 *= require select2
 *= require select2-bootstrap

application.js

//= require jquery
//= require jquery_ujs
//= require bootstrap
//= require turbolinks
//= require_tree .
//= require select2

Gemfile

gem 'bootstrap-sass'
gem 'select2-rails'

the problem, noticed the f.text_field :name not aligned with select_tag(:option