Explain about public and protected Access Modifiers?

Private:
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private is an access modifier for type members only. private access is the least accessible and such members are only accessible within the body of the containing type.
Note that nested types within the same containing body can also access those private members.

Internal:
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internal is an access modifier for types and type members. internal members are accessible only within file of the same assembly. It is an error to reference an internal type or internal type member outside the assembly within which it was declared.

A common use of internal access is in component-based development because it enables a group of components to interact in a private matter without being exposed to the outer world. For example, a Data Access Layer could have several classes with internal members that are only used by the DAL.
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Internal :

It can be accessed by any code in the same assembly but cannot be accessable in another assembly

Protected Internal :

It can be accessed by any code in the same assembly, or by any derived class in another assembly. For a particular project. (More...)

Public (More...)

Scope of public/private/friend/protected/protected friend.

Visual Basic/Visual C#
Public/public All members in all classes and projects.

Private/private Members of the current class only.

Friend/internal All members in the current project.

Protected/protected All members in the current class and in classes derived from this member's class. Can be used only in member definitions, not for class or module definitions.

Protected Friend/protected internal All members in the current project and all members in classes derived from this member's class. Can be used only in member definitions, not for class
or module definitions. (More...)

Access is limited to the current assembly or types derived from the containing class (More...)

We can access with in the project and also in the derived project (More...)

Access modifiers are keywords used to specify the declared accessibility of a member or a type. This section introduces the four access modifiers:
. Public - Access is not restricted.
. Protected - Access is limited to the containing class or types derived from the containing class.
. Internal - Access is limited to the current assembly.
. Protected inertnal - Access is limited to the current assembly or types derived . from the containing class.
. Private - Access is limited to the containing type.
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Public - Access to same assembly or another assembly that references it.

Private - Access to same class or struct.

Protected - Access to same class or struct, or in a class that is derived.

Internal - Access to any code in the same assembly, but not from another assembly.

Protected Internal - Access to any code in the assembly in which it is declared, or from within a derived class in another assembly.
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Event's are always public can be used where ever registered. But we can have access modifiers in events.Wecan have events with protected keyword which will be accessible only to inherited classes.We can have private events only for that class. (More...)

Active Directory Service Interfaces (ADSI) is a programmatic interface for Microsoft Windows Active Directory. It enables your applications to interact with diverse directories on a network, using a single interface. Visual Studio .NET and the .NET Framework make it easy to add ADSI functionality with the DirectoryEntry and DirectorySearcher components.

Using ADSI, you can create applications that perform common administrative tasks, such as backing up databases, accessing printers, and administering user accounts. (More...)