Understanding the Correct Syntax to Set Font-size in CSS

The question pertains to the correct syntax to set all the <a> tags' font-size to 13px in CSS (Cascading Style Sheets). CSS is a powerful language used for enhancing the look and formatting of the HTML structures. Let's go into the details on how to correctly apply CSS rules to HTML elements.

The correct answer is a{font-size:13px;}. This is a basic CSS rule that consists of a selector ('a' in this case), and a declaration block ({font-size: 13px;}). The selector determines which HTML elements the CSS rule will affect—in this case, all the <a> elements on the page. The declaration block contains one or more declarations separated by semicolons. Each declaration includes a CSS property name and a value, separated by a colon.

In the declaration font-size:13px;, 'font-size' is a CSS property that regulates the font size, and '13px' is the size value in pixels. The whole declaration is then concluded with a semicolon.

a {
  font-size: 13px;
}

This code will make the text inside all the <a> tags on the webpage display with a font size of 13 pixels.

The other options provided are incorrect because they do not follow the correct syntax for applying CSS rules.

• a {size: 13px;}: there is no 'size' property in CSS, so this would not change the font size.
• a {font-size: 13}: this is missing the 'px' needed to specify the unit of the font size.
• a:font-size(13px);: the syntax structure is incorrect. CSS uses braces {} to enclose declarations, and it does not use parentheses () for this purpose.

Best practices when writing CSS are to always add a semicolon after each declaration, even the last one, and include spaces for readability. Also, use comments to describe sections, especially in larger style sheets, and consider grouping similar sections of code together. These practices enhance the readability and maintainability of your CSS code.

In conclusion, implementing CSS rules is paramount in defining the stylistic layout of web pages, and doing so correctly can help achieve an aesthetically pleasing user interface. So, the correct syntax to set all the <a> tags' font-size to 13px is indeed a{font-size:13px;}.