In the following spelling question, four English words are given; choose the one that is incorrectly spelt and therefore needs correction in standard usage.

Introduction / Context:
This question focuses on spelling accuracy, a key component of language competence tested in many competitive exams. Candidates are often asked to identify which one among several given words is wrongly spelt according to standard English. Such questions not only test memory but also reward careful reading and familiarity with commonly used formal words in newspapers and academic texts.

Given Data / Assumptions:
Four words are provided: "Coalescence", "Complaisance", "Concomittant", and "Commissariat". We must identify which word is spelt incorrectly. We assume British or standard international spelling norms.

Concept / Approach:
The key to these questions is to recall or check the correct spelling of each word. "Coalescence" (coming together or merging) is correctly spelt. "Complaisance" (willingness to please) is also correctly spelt. "Commissariat" (a department responsible for food, supplies, or logistics) is correct as well. The word that stands out is "Concomittant", which has an extra "t". The correct spelling is "concomitant", with a single "t" in the middle.

Step-by-Step Solution:
Step 1: Examine each word slowly rather than skimming quickly. Step 2: Recall that "coalesce" leads to the noun "coalescence", which is correctly formed. Step 3: Remember that "complaisant" gives "complaisance", which matches Option B. Step 4: Recognise "concomitant" as the correct spelling, making "Concomittant" incorrect. Step 5: Verify that "Commissariat" is correctly spelt, leaving Option C as the wrong one.

Verification / Alternative check:
To verify, you can mentally break down "concomittant": the double "tt" after "mi" looks suspicious when compared with related forms such as "concomitant effect" or "concomitant circumstances", which you may have seen in reading. Consulting a dictionary would show "concomitant" as the only correct form. Since the other three words match standard spellings, we can confidently mark "Concomittant" as the incorrect spelling.

Why Other Options Are Wrong:
Option A, "Coalescence", correctly represents the process of coming together or uniting. Option B, "Complaisance", is the correct noun for a disposition to please others or be courteous. Option D, "Commissariat", correctly refers to a department responsible for providing food and supplies, particularly in an army or government. None of these words contains an extra or missing letter that would make the spelling wrong. Only Option C has the incorrect double "tt".

Common Pitfalls:
Candidates sometimes overthink such questions and assume that the least familiar word must be wrong. Others are tempted by double consonants in "commissariat" because the spelling looks complex. A good strategy is to mentally pronounce each syllable and compare it with prior reading. Building a personal list of frequently misspelt words, including "concomitant", will help reduce guessing and strengthen your spelling accuracy in the long run.

Final Answer:
The correctly identified incorrectly spelt word is "Concomittant".