We have a pick list on our web to lead form and I would like to add a validation on the field, we have validation on other field. 

Is someone could help out in adding a validation rule here for lead_source I will really appreciate

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      <p style="border-bottom: 1px solid grey;"></p>
      <input style="display:none" type="text" id="firstname" name="xxxxxxxxxx" size="40" autocomplete="off">

      <label for="first_name">First Name: <span style="color:darkred;">*</span><span style="float:right;">indicates
          required</span><span style="float:right;color:darkred;">*&nbsp;</span></label>
      <div id="VIPregistration_first_name_errorloc" class="form-error-text"></div><input id="first_name" maxlength="40"
        name="first_name" size="40" type="text" autocomplete="given-name">


      <label for="last_name">Last Name: <span style="color:darkred;">*</span></label>
      <div id="VIPregistration_last_name_errorloc" class="form-error-text"></div><input id="last_name" maxlength="80"
        name="last_name" size="80" type="text" autocomplete="family-name">


      <label for="email">Email: <span style="color:darkred;">*</span></label>
      <div id="VIPregistration_email_errorloc" class="form-error-text"></div><input id="email" maxlength="80" name="email"
        size="80" type="email" autocomplete="email">


      <label for="phone">Phone: <span style="color:darkred;">*</span></label>
      <div id="VIPregistration_phone_errorloc" class="form-error-text"></div><input id="phone" maxlength="18" minlength="10"
        name="phone" size="18" type="tel" autocomplete="tel" onkeydown="javascript:backspacerDOWN(this,event);" onkeyup="javascript:backspacerUP(this,event);" />
		
		
		<label for="lead_source">How did you hear about this opportunity?<span style="color:darkred;">*</span></label><select type="source" required="required" id="lead_source" name="lead_source">
              
              
              
              <option value="">--None--</option>
                           		
					<option value=" Condos -  Email Updates">Condos -  Email Updates</option>
					<option value="Google">Google</option>
					<option value="Bing">Bing</option>
					<option value="Facebook">Facebook</option>
					<option value="Instagram">Instagram</option>
					<option value="Twitter">Twitter</option>
					<option value="YouTube">YouTube</option>
					<option value="TV Ad">TV Ad</option>
					<option value="Radio Ad">Radio Ad</option>
					<option value="Flyer Ad">Flyer Ad</option>
					<option value="Referral">Referral</option>
					</select><br>

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  <script type="text/javascript">

  var frmvalidator = new Validator("VIPregistration");
    frmvalidator.EnableOnPageErrorDisplay();
    frmvalidator.EnableMsgsTogether();

    frmvalidator.addValidation("first_name", "req", "Please enter your First Name");
    frmvalidator.addValidation("first_name", "maxlen=40", "Our Apologies, First Name is Limited to 40 Characters Only");
    frmvalidator.addValidation("first_name", "alpha_s", "Name can Contain Alphabetic Characters Only");

    frmvalidator.addValidation("last_name", "req", "Please enter your Last Name");
    frmvalidator.addValidation("last_name", "maxlen=80", "Our Apologies, Maximum 80 Characters are Permitted for Your Last Name");

    frmvalidator.addValidation("email", "maxlen=80");
    frmvalidator.addValidation("email", "req", "Please enter your Email Address");
    frmvalidator.addValidation("email", "email");

    frmvalidator.addValidation("phone", "maxlen=18", "Please Enter Your 10 Digit Phone Number");
    frmvalidator.addValidation("phone", "req", "Please enter your Phone Number with Area Code");
    frmvalidator.addValidation("phone", "minlen=10", "Please Enter Your 10 Digit Phone Number");