<!-- default -->
<div class="form-check">
  <input class="form-check-input" type="radio" id="radio1" checked />
  <label class="form-check-label" for="radio1">Radio</label>
</div>

<!-- inline -->
<div class="form-check form-check-inline">
  ...
</div>

<!-- valid -->
<div class="form-check">
  <input class="form-check-input is-valid" />
</div>

<!-- invalid -->
<div class="form-check">
  <input class="form-check-input is-invalid" />
</div>