Select the word with the correct spelling from the following options.

Introduction / Context:
Spelling questions are a straightforward but important part of many competitive exams. They test your familiarity with common English words and your ability to spot incorrect letter patterns. Here, you must identify the correctly spelt word among four options, three of which contain deliberate spelling errors. Such questions improve your proofreading skills and help avoid mistakes in formal writing.

Given Data / Assumptions:

• The task is simply: "Select the word with the correct spelling."
• Options: chaastity, marothon, reasert, toxicity.
• Each option appears to resemble a real English word.
• Only one option is correctly spelled; the others contain errors.

Concept / Approach:
The strategy is to recognise the correct forms of familiar words. The four options approximate "chastity", "marathon", "reassert", and "toxicity". Knowing the correct spelling of these words allows you to eliminate the wrong forms. Because spelling rules in English are irregular, memory and exposure are crucial. You can often spot double letters or misplaced vowels that signal mistakes.

Step-by-Step Solution:
Step 1: Consider option "chaastity". It looks like a form of "chastity", a word meaning purity. The correct spelling is c h a s t i t y, with only one "a" after "ch". So "chaastity" with double "a" is incorrect. Step 2: Consider option "marothon". This resembles "marathon", the long-distance race. The correct spelling is m a r a t h o n, with "a" after "mar". "Marothon" with an "o" after "mar" is wrong. Step 3: Consider option "reasert". It looks like "reassert". The correct word meaning "state again" is r e a s s e r t, with double "s" in the middle. "Reasert" with one "s" is incorrectly spelled. Step 4: Consider option "toxicity". This word is commonly used in science and everyday English to mean the degree of being toxic or poisonous. The accepted spelling is t o x i c i t y, exactly as given here. Step 5: Conclude that "toxicity" is the only correctly spelled word among the four options.

Verification / Alternative check:
You can quickly verify by recalling where you may have seen each word. Marathon is frequently used in sports news, spelled as "marathon". Chastity appears in moral or religious texts as "chastity". The prefix "re-" plus the verb "assert" logically gives "reassert" with double "s". Toxicity appears in health advisories and scientific contexts, always spelled "toxicity". Cross-checking each option with known words confirms that only "toxicity" matches its correct form.

Why Other Options Are Wrong:

• chaastity: Incorrect because of the double "a". The real word is "chastity".
• marothon: Incorrect substitution of "o" for "a" after "mar". The correct spelling is "marathon".
• reasert: Missing an "s". The verb is "reassert", so its forms must preserve the double "s".

Common Pitfalls:
Students sometimes choose the longest or most complicated-looking word, assuming it is correct. Others are tricked by pronunciation and think that the sound of the word directly indicates spelling. English spelling often preserves historical patterns rather than phonetic ones, so regular reading and practice are more reliable than guesswork. In exams, always mentally compare each option with a word you have seen in books, articles or reliable sources.

Final Answer:
The correctly spelled word is toxicity.