Few Good questions : Any answers ?

Here are some good and very basic questions that were asked in a interview for the position of technical leads for a CMMI 5 level company in India . The interesting point is that 85% of the respondent could not answer even half of them...

Here are the some of those questions :
If readers have answers to these please put comment to this post :)

* What is the difference between System.Int32 type and int type?
* Can you assign null value to a struct?
* How does the modifier readonly affect reference types?
* Is this code valid public const object KEY = new object()?
* Do you need to have a catch block whenever you use the try block?
* What is the accessibility level of internal protected fields and methods?