I was able to solve my problem using jquery. I added a one additional field which would hides the 2 required options. I seperated both the input fields into 2 different divisions. and then I wrote the jquery code which would carryout the condition required.

View:

<select id="taxid" style="width:10%;">
                <option>Select TaxID Type</option>
                <option value="id1">ID1</option>
                <option value="id2">ID2</option>
            </select>
            <div id="feinfield">
                @Html.TextAreaFor(Model => Model.ID1, new { style = "width:50%; border-color: grey" })
                @Html.ValidationMessageFor(Model => Model.ID1)
            </div>
            <div id="ssnfield">
                @Html.TextAreaFor(Model => Model.ID2, new { style = "width:50%; border-color: grey" })
                @Html.ValidationMessageFor(Model => Model.ID2)
            </div>

jquery

<script>
        $(function () {
            $('#id1field').hide();
            $('#taxid').change(function () {
                if ($('#taxid').val() == 'id1') {
                    $('#id1field').show();
                } else {
                    $('#id1field').hide();
                }
            });
        });

        $(function () {
            $('#id2field').hide();
            $('#taxid').change(function () {
                if ($('#taxid').val() == 'id2') {
                    $('#id2field').show();
                } else {
                    $('#id2field').hide();
                }
            });
        });
    </script>

Let me know if you have any concerns/queries about my solutions.

I have 2 different fields in my Database named ID1 and ID2; and have a dropdown in my View with ID1 and ID2 to select.

My requirement is if the user choose ID1 in the Dropdown, then the textarefor ID1 field should populate/visible, and if the user choose ID2, Then the textarefor ID2 should be visible

I tried making a selection list in my Model class thinking I could write condition in my Controller class, but having issues while trying to call it in the view.

Is there a way I could make this condition work in my View directly?

View:

<select id="taxid" style="width:10%">
            <option value="id1">ID1</option>
            <option value="id2">ID2</option>
        </select>
@Html.TextAreaFor(Model => Model.ID1, new { style = "width:50%; border-color: grey"})
@Html.ValidationMessageFor(Model => Model.ID1)
@Html.TextAreaFor(Model => Model.ID2, new { style = "width:50%; border-color: grey"})
@Html.ValidationMessageFor(Model => Model.ID2)

Can someone help me with this?
Thank you