In the following question, four words are given. Out of these, select the word that is incorrectly spelt.

Introduction / Context:
This spelling question asks you to identify which of the four given words is incorrectly spelt. Spelling-based items test your familiarity with common English words as they appear in textbooks, newspapers and official documents. Recognizing incorrect spellings quickly can help avoid errors in written exams and formal writing.

Given Data / Assumptions:

• The four words are: Usable, Defense, Inventor, Annaul.
• Only one of these is spelt incorrectly.
• Standard British or Indian English spelling is assumed, but here the error is obvious in any variety of English.

Concept / Approach:
To answer this, you should mentally check each word against its correct spelling. “Usable”, “Defense” and “Inventor” are all correctly spelt words, although “defence” is the British variant and “defense” is the American variant. However, both forms are recognised. The word “Annaul” stands out as incorrect, because the correct spelling of the word meaning “yearly” is “Annual”.

Step-by-Step Solution:
Check “Usable”: correct spelling for something that can be used.Check “Defense”: American English spelling of “defence”; accepted in many contexts.Check “Inventor”: correctly spelt word meaning a person who invents things.Check “Annaul”: this appears to be a jumbled version of “annual”.The correct spelling is “Annual”, with “u” before “a” in the last syllable, not “Annaul”.

Verification / Alternative check:
Replace “Annaul” in a sample sentence: “The annaul sports day will be held in December.” This clearly looks wrong to any reader. Correcting it to “annual sports day” immediately reads correctly, confirming that “Annaul” is the incorrect spelling among the options.

Why Other Options Are Wrong:
“Usable” is standard. “Defense” is correct in American English, while “defence” is used in British English; exam setters generally accept this spelling as correct. “Inventor” is also a standard spelling. Thus, none of these three words contain a spelling mistake, so they cannot be the answer in a spelling error question.

Common Pitfalls:
Students sometimes overthink such questions and suspect minor regional variations like “defense/defence” instead of spotting obvious jumbled spelling errors. Always look for clear mistakes such as wrong letter order or extra letters before worrying about English variants.

Final Answer:
The incorrectly spelt word is Annaul (correct spelling: “annual”).