In the following question, four words are given, out of which one word is incorrectly spelt. Select the incorrectly spelt word.

Introduction / Context:
This spelling question again asks you to spot the one incorrectly spelt word out of four options. The words here include one medical term and three general vocabulary items. Recognising correct spellings is important in professional writing and in understanding exam passages accurately.

Given Data / Assumptions:

• Options: Anasthetic, Obliterate, Concurrence, Blithesome.
• Exactly one spelling is wrong.
• We use standard British spelling for the medical word.

Concept / Approach:
The medical term for a drug that causes loss of sensation is anaesthetic (British English) or anesthetic (American English). In both cases, the form given in the question, Anasthetic, is incorrect: it is missing the sequence ae or e after n and misplaces the letters. Obliterate, Concurrence and Blithesome are correctly spelt words: obliterate means to destroy completely, concurrence means agreement, and blithesome means cheerful or lighthearted.

Step-by-Step Solution:
Check Anasthetic: the standard British spelling is anaesthetic (A N A E S T H E T I C) and the American spelling is anesthetic (A N E S T H E T I C). The given form Anasthetic does not match either; letters are missing and out of order.Check Obliterate: correctly spelt O B L I T E R A T E.Check Concurrence: correctly spelt C O N C U R R E N C E.Check Blithesome: correctly spelt B L I T H E S O M E, meaning cheerful.Thus, Anasthetic is the incorrectly spelt option.

Verification / Alternative check:
Think of common phrases: “under anaesthetic”, “local anaesthetic”, “general anaesthetic”. In each phrase, you will see anaesthetic or anesthetic with the full vowel pattern, not “Anasthetic”. Spelling lists and medical charts never use the faulty version, confirming that the question's option is wrong.

Why Other Options Are Wrong:
Obliterate is a common word in academic and journalistic writing, always spelt as shown. Concurrence appears in formal contexts, meaning agreement, as in “by common concurrence”. Blithesome, though less common, is spelled correctly and found in descriptive or literary English. Since these three conform to standard spelling, they cannot be the incorrect choice here.

Common Pitfalls:
Technical and scientific terms derived from Greek or Latin often cause spelling confusion because of clusters like ae, ph, and th. Exams deliberately include such words to test careful reading. When you see a difficult looking word, do not automatically assume it is wrong; instead, recall any medical terms or textbook phrases you know. Here, remembering anaesthetic or anesthetic makes it easy to recognise Anasthetic as a misspelling.

Final Answer:
The incorrectly spelt word is Anasthetic; the correct spelling is “anaesthetic” (British) or “anesthetic” (American).