XPath mentioned in Solution 1 by Sandeep
Mewara
is a good option.
Alternatively LINQ can be used as follows
string xmlText =@"<?xml version=""1.0"" standalone=""yes""?>
<LiveChat>
<Detail>
<Id>1</Id>
<Adver>STD</Adver>
<BitVer>32</BitVer>
<BtnScrn>HLC</BtnScrn>
<IsLiveChat>Y</IsLiveChat>
</Detail>
<Detail>
<Id>2</Id>
<Adver>STD</Adver>
<BitVer>64</BitVer>
<BtnScrn>HLC</BtnScrn>
<IsLiveChat>Y</IsLiveChat>
</Detail>
<Detail>
<Id>3</Id>
<Adver>STD</Adver>
<BitVer>32</BitVer>
<BtnScrn>FLC</BtnScrn>
<IsLiveChat>Y</IsLiveChat>
</Detail>
<Detail>
<Id>4</Id>
<Adver>STD</Adver>
<BitVer>64</BitVer>
<BtnScrn>FLC</BtnScrn>
<IsLiveChat>Y</IsLiveChat>
</Detail>
</LiveChat>";
XDocument liveChat = XDocument.Parse(xmlText);
XElement defaultDetail = new XElement ("Detail",
new XElement ("IsLiveChat", "N"));
string isLiveChatVal= (liveChat.Root.Elements().FirstOrDefault (r =>
r.Element("Adver").Value=="STD" &&
r.Element("BitVer").Value=="64" &&
r.Element("BtnScrn").Value=="FLC") ?? defaultDetail)
.Element("IsLiveChat").Value;