In this spelling question, four words are given, and you must identify the one word that is incorrectly spelt according to standard English usage.

Introduction / Context:
This spelling question requires you to pick out the one incorrectly spelt word among four options. The other three words are correctly spelt common English words that you will have encountered in textbooks and everyday reading. Spotting the wrongly spelt word depends largely on your visual memory of words and basic familiarity with English vocabulary.

Given Data / Assumptions:

• Options: "Dictionory", "Irrelevant", "Perishable", "Tangible".
• We are told that only one of these words is incorrectly spelt.
• The likely intended correct forms are "dictionary", "irrelevant", "perishable", and "tangible".

Concept / Approach:
The word "dictionary" is a very common English word referring to a reference book containing words and their meanings. Its correct spelling uses "a" before the final "ry" and not "o". The other three words, "irrelevant", "perishable", and "tangible", are correctly spelt in the options. Therefore, the misspelt word is "Dictionory", which replaces "a" with "o" in the second last syllable.

Step-by-Step Solution:
Step 1: Examine "Dictionory". The common word is "dictionary", which you see in book titles such as "Oxford English Dictionary". The correct sequence is "tionary", not "tionory". Hence "Dictionory" is wrong. Step 2: Look at "Irrelevant". This is spelt with double r and single l, exactly as it appears in standard English. There is no error here. Step 3: Check "Perishable". This word describes something that can decay or spoil, such as perishable goods. Its spelling with "perish" plus "able" is correct. Step 4: Review "Tangible". This means something that can be touched or physically felt. The spelling "tangible" is the standard dictionary form. Step 5: Conclude that "Dictionory" is the only incorrectly spelt option.

Verification / Alternative check:
You can verify this by writing the words as you have typically seen them. For instance, school children often write "dictionary work" or "dictionary meaning". If you imagine a book cover, you will recall the spelling "dictionary", not "dictionory". The other three words can be checked by dividing them into roots and suffixes: "ir" plus "relevant", "perish" plus "able", and "tang" plus "ible". All of these follow common English spelling patterns.

Why Other Options Are Wrong:
"Irrelevant" is a standard word meaning not related to the subject, and its spelling is correct.

"Perishable" correctly describes items that can rot or spoil and follows the typical formation pattern of adding "able" to a verb.

"Tangible" is correctly spelt and is frequently used in law and business contexts for things that have a physical presence.

Common Pitfalls:
Learners sometimes second guess themselves because all options look familiar. A good strategy is to silently pronounce each part of the word and recall where you have seen it. Words ending with "ary" such as "dictionary", "vocabulary", and "imaginary" follow a pattern that you can memorise. Mixing "ory" and "ary" is a common spelling mistake that exam makers like to test. Keeping a mental or written list of such common traps is useful for fast recognition in the exam hall.

Final Answer:
The incorrectly spelt word is "Dictionory"; the correct spelling is "dictionary".