Internet addressing – spotting an invalid domain example Which of the following strings is <em>not</em> a validly structured domain name according to common Internet naming conventions (letters/digits/hyphens in labels and a proper top-level domain)?

Introduction / Context:
Domain names are hierarchical. From right to left you have the top-level domain (TLD), the second-level domain, then optional subdomains. Valid examples end with a recognized TLD such as .com, .org, .net, or a country code like .uk and .fr.

Given Data / Assumptions:

• Capitalization is irrelevant (DNS is case-insensitive); focus on structure.
• “www” is a conventional subdomain label, not a requirement.
• We assume standard public DNS naming practices.

Concept / Approach:
A structurally valid domain must terminate in a TLD. For example, yahoo.com ends with .com (TLD). yahoo.co.uk ends with .uk (TLD) preceded by .co (a second-level category used by the UK registry). yahoo.fr ends with .fr (TLD). The string www.fr.yahoo ends with .yahoo, which is not the TLD in public DNS for that brand; instead, “yahoo” is widely known as a second-level domain under .com, .co.uk, .fr, etc. Without a valid TLD at the far right, the name is malformed for standard resolution.

Step-by-Step Solution:
Check the rightmost label in each option.Confirm a recognized TLD (.com, .uk, .fr) appears at the far right for valid domains.Identify “Www.fr.yahoo” → rightmost label “yahoo” is not a TLD here → invalid.

Verification / Alternative check:
Basic DNS resolution rules specify matching from the root rightward; the ultimate suffix must be a recognized TLD. The options with .com, .co.uk, and .fr satisfy this; the one ending in “.yahoo” does not.

Why Other Options Are Wrong:

• Www.yahoo.com : valid format, TLD .com.
• Www.yahoo.co.uk : valid UK multi-level domain format.
• Www.yahoo.fr : valid format with TLD .fr.

Common Pitfalls:
Thinking “www” is mandatory or that subdomain ordering is arbitrary. The TLD must always be the rightmost label.

Final Answer:
Www.fr.yahoo