There is no such limit.So you can have any.But If you need to find the maximum number of attributes on a node in your xml doc,Then you can use something is as below.
XElement el = XElement.Load("MyXML.xml");
int maxAttr = el.DescendantNodesAndSelf().OfType<XElement>().Max(x => x.Attributes().Count());
For more info :
Maximum number of attributes a node has in a XML document
I hope this will help to you.