using System;

using System.Xml;

public class Program

{

    public static void Main()

    {

        var xmlInput = @"<?xml version=""1.0"" encoding=""utf-8""?>

<Root>

  <Variable>

    <IsChecked>False</IsChecked>

    <ID>A</ID>

    <Description></Description>

  </Variable>

  <Variable>

    <IsChecked>True</IsChecked>

    <ID>B</ID>

    <Description></Description>

  </Variable>

  <Variable>

    <IsChecked>False</IsChecked>

    <ID>C</ID>

    <Description></Description>

  </Variable>

</Root>";

        XmlDocument xmlDoc = new XmlDocument();

        xmlDoc.LoadXml(xmlInput);

        var xmlItem = xmlDoc.SelectSingleNode("/Root/Variable[1]/IsChecked");

        Console.WriteLine(xmlItem?.InnerXml ?? "NULL");

    }

}