Include empty responses in form - html

Question

I am trying using HTML, Jquery, and Node.js to develop an online test for my students. Currently, when I submit the form, the server gets a json object (using body-parser) that includes only the fields that were answered. However, I also need to be able to see which ones were not answer. For example, if my student answers questions 1, 2, 3 but not 4, the server shows the following:
{Q1: a, Q2:b, Q3:c}
I want to get:
{Q1: a, Q2:b, Q3:c, Q4:''}
I tried looking online, however most posts explain how to get rid of the empty responses and not how to include them.
This is what I have right now
<div id="FormContainer1" class="container">
<form id="Form1" action="/Form1" method="POST">
<div class="row">
<div class="col">
<div class="row">
<label> 1. </label>
<label>A </labe> <input type="radio" name="Q1" value="A">
<label>B </labe> <input type="radio" name="Q1" value="B">
<label> C </labe> <input type="radio" name="Q1" value="C">
<label> D </labe> <input type="radio" name="Q1" value="D">
</div>
<div class="row">
<label> 2. </label>
<label> A </labe> <input type="radio" name="Q2" value="A">
<label> B </labe> <input type="radio" name="Q2" value="B">
<label> C </labe> <input type="radio" name="Q2" value="C">
<label> D </labe> <input type="radio" name="Q2" value="D">
</div>
<div class="row">
<label> 3. </label>
<label> A </labe> <input type="radio" name="Q3" value="A">
<label> B </labe> <input type="radio" name="Q3" value="B">
<label> C </labe> <input type="radio" name="Q3" value="C">
<label> D </labe> <input type="radio" name="Q3" value="D">
</div>
<div class="row">
<label> 4. </label>
<label> A </labe> <input type="radio" name="Q4" value="A">
<label> B </labe> <input type="radio" name="Q4" value="B">
<label> C </labe> <input type="radio" name="Q4" value="C">
<label> D </labe> <input type="radio" name="Q4" value="D">
</div>
</div>
</div>
</div>
<div class="row">
<div class="col">
<input type="submit" value="Submit">
</div>
</div>
</form>
and in the server I have,
app.post('/Form1', urlencodedParser, function(request,response){ console.log(request.body); })

Answer 1

You could add a hidden radio button for each question that is marked as checked:
<input type="radio" name="Q4" value="" style="display: none;" checked>