Make user check all answers on form

Is there a way to modify my database-powered quiz so that, if a user doesn't answer one or more questions, clicking the Submit button will trigger an alert? In other words, I want to force users to answer all the questions, even if they just guess. The scoring mechanism doesn't work correctly unless all the questions have a response.

Note that some questions (the last one in this example) may have multiple correct answers. I think all that matters is that at least one checkbox is selected.

<form action="" method="post" id="quiz">

  <li id="q9">
    <div class="Question">Scientists believe the universe is:</div>
    <div class="Answer">
      <label class="Wide" for="q9-A"><div class="Radio"><input type="radio" name="q9[]" id="q9-A" value="A" style="display: none;"> A. disappearing</div></label></div>
    <div class="Answer">
      <label class="Wide" for="q9-B"><div class="Radio"><input type="radio" name="q9[]" id="q9-B" value="B" style="display: none;"> B. expanding</div></label></div>
    <div class="Answer">
      <label class="Wide" for="q9-C"><div class="Radio"><input type="radio" name="q9[]" id="q9-C" value="C" style="display: none;"> C. contracting</div></label></div>
    <div class="Answer">
      <label class="Wide" for="q9-D"><div class="Radio"><input type="radio" name="q9[]" id="q9-D" value="D" style="display: none;"> D. becoming bipolar</div></label></div>
  </li>
  <li id="q10">
    <div class="Question">Check each item that can be found in our solar system.</div>
    <div class="Answer" style="margin-top: 5px; background: #000; color: #fff; text-align: center;">
    <label for="q10-A"><input type="checkbox" name="q10[]" id="q10-A" value="A">planet</label>
       <label for="q10-B"><input type="checkbox" name="q10[]" id="q10-B" value="B">asteroid</label>
       <label for="q10-C"><input type="checkbox" name="q10[]" id="q10-C" value="C">comet</label>
       <label for="q10-D"><input type="checkbox" name="q10[]" id="q10-D" value="D">black hole</label>
       <label for="q10-E"><input type="checkbox" name="q10[]" id="q10-E" value="E">neutrino star</label>
       <label for="q10-F"><input type="checkbox" name="q10[]" id="q10-F" value="F">quasar</label>
     </div>
      </li>
 </ol>
 <input type="hidden" name="PreviousURL" id="url" />
 <input type="hidden" name="user_token" value="54f3f5438292e" />
 <input type="submit" value="Submit Quiz" />
</form>