Actually, how do i write a 3d windows 8 game ?????? and also is there any way to do it in Unity....I know the way of writing it with JS or C# or C++ but still any engine out there

At the moment you have the following options for Windows 8 store apps:

• c++ with DirectX
• c#/vb.net, c++ and XAML
• HTML5 and JavaScript
• C# and MonoGame

Unity support is reportedly in the pipeline, but has no public release date and news seems to be a little quiet as of late.

If you're familiar with things such as XNA, then MonoGame is a nice option, but it's not an 'engine'.

It's worth noting that most Engines support Windows 8, but not for Windows 8 store apps.