Looping through models content in Razor

Yes, this is easy to do using the Linq GroupBy. I'd suggest changing your view to use @model IEnumerable<IGrouping<string, MyModel>>, which you'd populate like this:

var groupModel = MyModelCollection.GroupBy(item => item.GroupNo).ToArray();
return View(groupModel);

Then, simply iterate through the group as you wrote, except using group.Key instead of group.GroupNo to retrieve IGrouping's key:

@foreach (var group in Model) {
    <section>
        <header>Group No is @group.Key</header>
        @foreach (var item in group) {
            <p>GroupName: @item.GroupName</p>
        }
    </section>
} 

LINQ can help you do that

@model IEnumerable<Project1.Models.Group>


@foreach (var item in Model.Select(i=>i.groupno).Distinct().ToList()) {
    <tr>
        <td>
            <header>Group No is @item</header>
            @foreach (var grpName in Model.Where(i => i.groupno == item).ToList())
            {
                <p>GroupName: @grpName.groupName</p>
            }
        </td>
    </tr>
}