In ASP.NET AJAX 4.0, how many specialized validation controls are available and what is their general purpose?

Introduction / Context:
This question focuses on validation support in ASP.NET AJAX 4.0. In addition to standard ASP.NET validators, the AJAX Control Toolkit adds several extender controls related to validation and user input. Interview questions often ask you to recall how many such controls exist and what they broadly do.

Given Data / Assumptions:

• The environment is ASP.NET AJAX 4.0 with the AJAX Control Toolkit.
• We are interested in validation related extender controls.
• The controls typically attach to standard ASP.NET controls such as TextBox or validators.
• We want the total count and high level purpose.

Concept / Approach:
ASP.NET AJAX 4.0 provides several specialized controls that help with validation and input quality. These include FilteredTextBoxExtender, MaskedEditExtender, MaskedEditValidator, ValidatorCalloutExtender, NoBot, and PasswordStrengthExtender. Together they form six validation related controls that either restrict input patterns, display validation messages more clearly, prevent automated submissions, or measure password strength.

Step-by-Step Solution:
Step 1: List the known validation related controls: FilteredTextBoxExtender, MaskedEditExtender, MaskedEditValidator, ValidatorCalloutExtender, NoBot, and PasswordStrengthExtender. Step 2: Count these controls to determine there are six in total. Step 3: Recognise that they extend or wrap existing ASP.NET controls to improve input filtering, masking, and validation feedback. Step 4: Select the option that states there are six validation related controls with this general purpose.

Verification / Alternative check:
You can verify this by checking typical ASP.NET AJAX interview question collections and tool documentation, where these six controls are listed together as validation or input related extenders. They are not meant to replace all standard validators but to enhance and support them with better user experience and additional checks.

Why Other Options Are Wrong:
Option b: Claims there is only one validation control, which is incorrect because the toolkit clearly defines multiple distinct extenders.

Option c: States there are ten controls and incorrectly ties them to specific HTML tags, which does not reflect the real design of the toolkit.

Option d: Suggests that ASP.NET AJAX 4.0 provides no validation controls, which contradicts the actual list of extenders provided.

Common Pitfalls:
A frequent mistake is to confuse the standard ASP.NET validation controls with AJAX specific ones. Standard validators such as RequiredFieldValidator exist independently of the AJAX toolkit. Another pitfall is to forget that some of these controls, like ValidatorCalloutExtender, primarily enhance the user interface of validation messages rather than performing the validation logic themselves.

Final Answer:
ASP.NET AJAX 4.0 provides six specialized validation related controls that extend or enhance standard validation behavior, including controls for filtering input, masking formats, improving error display, preventing automated submissions, and measuring password strength.