In PHP, should you initialise string literals with single quotes or double quotes, and what practical difference does this choice make?

Introduction / Context:
PHP supports both single quoted and double quoted string literals, but they are not processed in exactly the same way. The choice between them affects how PHP interprets variables and escape sequences inside the string. This question checks whether you understand when each style is appropriate and what effect it has on the resulting string.

Given Data / Assumptions:

• We are writing PHP code that contains string literals.
• Some strings may need variable interpolation or special escape sequences, while others are simple text constants.
• Performance differences between the two forms are small but often mentioned in discussions.

Concept / Approach:
Double quoted strings in PHP support variable interpolation and a wider set of escape sequences. If you write "Hello $name", PHP replaces $name with its value. It also interprets sequences like for newline. Single quoted strings treat most characters literally. Variables inside single quotes are not expanded, and only a few escapes such as \\' and \\\\ have special meaning. As a result, single quoted strings are slightly simpler for the engine to parse and are ideal when you do not need interpolation. Developers often choose single quotes for pure literals and double quotes when they want dynamic content inside the string.

Step-by-Step Solution:
Step 1: Recall that "Hello $name" will output the value of $name, but '\'Hello $name\' will output the literal dollar sign and variable name.Step 2: Recognise that double quotes interpret escape sequences such as "" as actual newlines, while single quotes leave them as backslash followed by n in most cases.Step 3: Note that single quotes require fewer parsing steps from PHP, which can be marginally faster but mainly improves clarity for literals.Step 4: Based on this behaviour, the recommended practice is to use single quotes for constant strings and double quotes when you need interpolation or expressive escapes.Step 5: Option A expresses this practical guideline accurately and is therefore the correct answer.

Verification / Alternative check:
Testing echo "LineNext"; will output two lines, while echo '\'LineNext\'; will show the backslash and n characters literally. Similarly echo "Value: $x"; will show the value of $x, while echo '\'Value: $x\'; will not. This demonstrates the core difference between the two quoting styles.

Why Other Options Are Wrong:
Option B incorrectly claims that single quotes are reserved only for database queries, which is not true. Option C states that double quotes are illegal, which is false. Option D claims there is no difference, which contradicts both documentation and observable behaviour in any simple test.

Common Pitfalls:
One pitfall is accidentally placing variables inside single quoted strings and then wondering why they are not expanded. Another is mixing quotation styles in nested contexts and forgetting to escape them properly. Adopting a consistent guideline, such as single quotes for literals and double quotes for strings with variables, helps keep code readable and avoids subtle bugs.

Final Answer:
Prefer single quotes when no variable interpolation or special escape sequences are needed, because PHP treats them slightly more simply, and use double quotes when you want variables or certain escapes to be interpreted inside the string.