Silverlight supports Windows Media Audio and Video (WMA, WMV7-9) and VC-1, as well as MP3 audio.

A basic xap file in silverlight will have an assembly related to specific code for the application, an application manifest file and any additional assemblies need to run the application. At a minimum, two files are needed, the application manifest file and the application assembly. For example:

AppManifest.xaml
MyPianoV2.dll

Once you have created the .xap file, the Silverlight 2 or 3 plug-in downloads the file and runs it in a separate work space.

A .xap file is used to contain and transfer the assemblies and resources of a managed code application. This managed code application must be run within the Silverlight 2 browser plug-in.

Application.Current.Host.Content.IsFullScreen=true;

RIA Services is a library of client and server components that bolt on to ADO.NET Data Services. When the full stack of RIA Services is used the difference between RIA Services and plain WCF are as follow:

1.The client side data objects are generated using reflection at compile time based on the actual server side objects instead of a service contract. This allows RIA Services to provide a much richer client side object model by including any business rules and relationships between objects. However, this does mean that RIA Services gives up some flexibility compared to plain WCF. For example, the RIA Services serializaer does not currently support some data types which WCF would be able to handle.

2.RIA Services, like ADO.NET Data Services, supports serializing LINQ queries between the client and the server. This means that the client can create the LINQ query and have it run server side.

3.RIA Services, unlike plain ADO.NET Data Services, does not automatically generate CRUD at runtime. For people familiar with SQL Server, I describe ADO.NET Data Services as supporting regular triggers (aka query interceptors) while RIA Services requires INSTEAD OF triggers.

Deep zoom helps to view high resolution images in silverlight application, using deep zoon one can zoom in and out with out affecting the performance of the application.

Deep zoom composer helps to create high resolution images for panning and smooth zooming.

No, It's a cross platform version of the .NET Framework which is included in the 6 MB Silverlight 4 download, so you do not need to have anything extra to be installed on the client in order to access Silverlight applications in the browser.

Microsoft .NET RIA Services provides support to make the n-tier application pattern by combining the ASP.NET and Silverlight platforms in a simple manner.
RIA Services presents a pattern which a help of that you can write application logic that can run on the mid-tier and controls access to data for queries, changes, and custom operations.
It support data validation, authentication, and roles by integrating with Silverlight components on the client and ASP.NET on the middle tier.

There are three controls available, they are;

StackPanel - this will position the child elements either in horizontal or in a vertical manner.

Grid - This will position the child elements in either columns or rows.

Canvas - This will position the child elements according to X,Y space.

It compel cross-platform user experiences.
It has Flexible programming model with collaboration tools.
It outputs High-quality media and with a low-cost delivery.
It can be Connected to data, servers, and services.

In a simple way we can set the default page, what we have to do is to change the default page of a silverlight application, we have to set the RootVisual property inside the Application_Startup event of the App.xaml file.