LINQ (Language Integrated Query) is an expression that retrieves data from a data source. LINQ simplifies this situation by offering a consistent model for working with data across various kinds of data sources and formats. In a LINQ query, you are always working with objects. You use the same basic coding patterns to query and transform data in XML documents, SQL databases, ADO.NET Datasets, .NET collections, and any other format for which a provider is available. LINQ can be used in C# and VB.
ADO(ActiveX Data Objects).Net is a tool provided by Microsoft which provides access to data sources such as SQL Server, Oracle, and XML through its components. .Net front-end applications can retrieve, create, and manipulate data, once they are connected to a data source through ADO.Net with appropriate privileges.
ADO.Net provides a connection-less architecture. It is a secure approach to interact with a database, since, the connection doesn't have to be maintained during the entire session.