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how to send boolean with newselectList from cshtml in form C#

You can try something like here:

<%= Html.DropDownList(
    "", 
    new SelectList(
        new[] 
        { 
            new { Value = "true", Text = "Yes" },
            new { Value = "false", Text = "No" },
        }, 
        "Value", 
        "Text",
        Model
    )
) %>