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

Introduction / Context:
Accurate spelling is crucial in English, especially for formal writing and competitive exams. This question asks you to identify the one incorrectly spelt word among four commonly used terms. Such questions usually target words whose pronunciation can mislead the learner about the correct arrangement of vowels and consonants.

Given Data / Assumptions:

• Words given: Secondary, Sizable, Succumb, Sustanence, Sanction.
• Exactly one word is misspelt.
• The others follow standard dictionary spellings.
• The focus is on noticing incorrect vowel combinations.

Concept / Approach:
The word that stands out here is "Sustanence". The correct noun meaning "food and drink regarded as a source of strength" or "means of support" is spelt "sustenance". The vowel pattern is s-u-s-t-e-n-a-n-c-e, not "a-n-e-n" as in the incorrect option. The other words—secondary (of second rank or importance), sizable (fairly large), succumb (yield or give way), and sanction (official approval or penalty)—are all correctly spelt and frequently used in written English.

Step-by-Step Solution:
Step 1: Check "Secondary". The spelling s-e-c-o-n-d-a-r-y is standard and correct.Step 2: Check "Sizable". Both "sizable" and "sizeable" are accepted variants; here "Sizable" is correctly spelt in standard American and widely used international English.Step 3: Check "Succumb". The correct spelling is s-u-c-c-u-m-b, and the option matches it.Step 4: Check "Sustanence". This looks suspicious because the familiar word is "sustenance".Step 5: Confirm that the correct spelling is s-u-s-t-e-n-a-n-c-e, so "Sustanence" with "a-n-e-n" is wrong.Step 6: Check "Sanction". It is correctly spelt s-a-n-c-t-i-o-n.Step 7: Conclude that "Sustanence" is the only incorrectly spelt word.

Verification / Alternative check:
We can test by using the suspect word in a sentence: "The army received fresh sustenance from the nearby village." Any dictionary will show this exact spelling: sustenance. Spell checkers in word processors also flag "sustanence" as incorrect. In contrast, "secondary school", "sizable amount", "succumb to pressure", and "economic sanctions" all appear with these spellings in respectable newspapers and books, confirming that those four options are correct.

Why Other Options Are Wrong:
In this particular problem, "wrong" options are the correctly spelt words. "Secondary" is correct and widely used. "Sizable" is an accepted spelling. "Succumb" matches the dictionary form. "Sanction" is also standard. Only "Sustanence" fails to match the correct form "sustenance", so it is the misspelt word you must select.

Common Pitfalls:
Learners often struggle with silent letters like the "b" in "succumb" or the choice between "sizable" and "sizeable". Because of this, they may wrongly suspect those words instead of noticing the vowel pattern problem in "Sustanence". A good method is to pay attention to root words and related forms: "sustain" leads to "sustenance", keeping "sust-" and "-tenance" rather than "sustanence". Building small families of words in your vocabulary notebook helps reinforce both meaning and spelling.

Final Answer:
The incorrectly spelt word is "Sustanence".