Which of the following is not a difference between HTML and XHTML

Option A is the correct answer.

The question asks for the statement that is not a valid difference between HTML and XHTML. Option A is incorrect because it contains factual errors. It refers to text/html and application/xml+xhtml as character sets (charsets), whereas they are actually MIME (Content) Types. In addition, the correct MIME type for XHTML is application/xhtml+xml, not application/xml+xhtml. Since the statement itself is incorrect, it cannot be considered a valid difference between HTML and XHTML.

Why Option B is incorrect:

Option B states "None of the mentioned", which would be correct only if all the other options described valid differences. However, Option A is factually incorrect, so not all the listed statements are valid differences. Therefore, Option B cannot be the correct answer.

Why Option C is incorrect:

Option C states that tags and attributes are case-insensitive in HTML but not in XHTML. This is a genuine difference. HTML parsers generally treat tag and attribute names without regard to case, whereas XHTML follows XML rules and is case-sensitive. For example, <BODY> is accepted in HTML, but XHTML requires <body>. Since this statement correctly describes a difference, it is not the answer.

Why Option D is incorrect:

Option D states that special characters must be escaped using character entities in XHTML. XHTML is based on XML and therefore follows strict XML syntax rules. Characters such as &, <, and > must be escaped wherever required to ensure the document is well-formed. HTML is generally more forgiving and may tolerate certain unescaped characters in situations where XHTML would produce a parsing error. Therefore, this option also describes a valid difference.

Hence, Option A is the only statement that is not a valid difference because it incorrectly describes MIME types as charsets and uses an invalid MIME type for XHTML.