In PHP, what are superglobal variables and what special property do they have compared with normal variables?

Introduction / Context:
PHP provides a number of predefined variables that give access to request data, server information, environment variables, uploaded files, and session state. Many of these are grouped into arrays called superglobals. Superglobals are a distinctive feature of PHP because they behave differently from normal variables in terms of scope. This question asks you to define superglobal variables and describe their special property so that you can use them correctly in your code.

Given Data / Assumptions:

• PHP scripts often contain functions and methods that introduce local scopes.
• Normal global variables must be imported into functions using the global keyword.
• Superglobal variables have names such as $_GET, $_POST, $_SESSION, and $_SERVER.
• We are interested in how scope rules apply to these predefined variables.

Concept / Approach:
In PHP, a superglobal is a predefined array that is automatically available in all scopes. Unlike ordinary globals, you do not need to declare them with the global keyword inside functions. Examples include $_GET for query parameters, $_POST for form data, $_COOKIE for cookies, $_SESSION for session data, $_FILES for uploads, $_SERVER for server context, and $_ENV for environment variables. The special property of superglobals is this automatic global availability, which makes it easy to access request and environment data from any part of the script without extra plumbing.

Step-by-Step Solution:
Step 1: Identify that superglobal variables are predefined by PHP and have names that typically start with an underscore and uppercase letters.Step 2: Recognise that they are arrays holding structured data about requests, sessions, cookies, and the server environment.Step 3: Note that they are accessible in any scope, including inside functions and methods, without using the global keyword.Step 4: Compare this with normal global variables, which require explicit global declarations inside functions to be visible there.Step 5: Conclude that the special property of superglobals is their automatic scope, which simplifies working with request and environment data.

Verification / Alternative check:
To confirm this behaviour, create a PHP script that defines a normal global variable and also uses $_GET. Inside a function, attempt to echo the normal global variable without the global keyword; it will not be visible. Then echo $_GET inside the same function, and it will be available. Adding the global declaration for the normal variable will make it visible, highlighting the difference between regular globals and superglobals. This simple test confirms the unique scope behaviour of superglobals.

Why Other Options Are Wrong:
Option B says superglobals can only be used inside user defined classes, which is incorrect; they can be used anywhere. Option C suggests that they are automatically saved to disk after every request, but persistence is instead handled by mechanisms such as sessions or databases. Option D claims they are constants that never change at runtime, which is false because their contents change for each request and user. These descriptions do not match the real definition and behaviour of superglobal variables.

Common Pitfalls:
One pitfall is overusing superglobals directly throughout an application, which can make code harder to test and maintain. A better approach is often to read values from superglobals at the edges of the application and inject them into functions as parameters. Another issue is assuming that superglobal data is safe and trustworthy. All input should be validated and sanitised, even though it arrives through convenient superglobal arrays. Keeping these points in mind helps you leverage superglobals effectively while still writing clean and secure PHP code.

Final Answer:
Correct answer: They are predefined global arrays that are available in all scopes without using the global keyword