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 asks you to identify the incorrectly spelt word from a group of four. Spelling questions test your familiarity with common English words that are widely used in newspapers, legal contexts and everyday conversation. Here, the words relate to legal terminology and common nouns. You must recognise which spelling does not match the standard dictionary form. Correct spelling is especially important in written exams, descriptive papers and professional communication.

Given Data / Assumptions:

The four options are “pedestrain”, “plaintiff”, “potatoes” and “potassium”.
Three of these are correctly spelt common words.
One option contains a spelling error that you must identify.
We assume standard British or Indian English spellings, which match these forms for the correct words.

Concept / Approach:
The standard spelling for a person who walks on the road is “pedestrian”, not “pedestrain”. The given option “pedestrain” has the letters “a” and “i” in the wrong order and is therefore incorrect. The other words are spelled correctly: “plaintiff” (a person who brings a legal case), “potatoes” (plural of potato, with “-es”) and “potassium” (a chemical element). The approach is to mentally compare each option with its known correct spelling and locate the one that does not match.

Step-by-Step Solution:
Step 1: Examine “pedestrain”. The intended word appears to be “pedestrian”. Step 2: The correct spelling “pedestrian” has the sequence “-trian”, not “-train”, so “pedestrain” is wrong. Step 3: Check “plaintiff”. This is correctly spelt as p-l-a-i-n-t-i-f-f. Step 4: Check “potatoes”. The plural of potato adds “-es”, so “potatoes” is the correct spelling. Step 5: Check “potassium”. This is the correct spelling of the chemical element symbol K in the periodic table. Step 6: Conclude that “pedestrain” is the only wrongly spelt word.

Verification / Alternative check:
Look up or recall familiar usage. “Pedestrian crossing”, “pedestrian bridge” etc. always use “pedestrian”. There is no recognised English word “pedestrain” in standard usage. On the other hand, “plaintiff” is a common word in legal news, and “potatoes” appears frequently in everyday writing, while “potassium” is a standard scientific term. Spelling patterns like “-es” for nouns ending in “-o” (potato → potatoes) and double “f” in “plaintiff” are well-established. This cross-check confirms that “pedestrain” is incorrect.

Why Other Options Are Wrong (as answers):
Plaintiff: Correct spelling; refers to the person who initiates a lawsuit in a court of law.
Potatoes: Correct spelling; plural of “potato” according to the normal rule of adding “-es” to many nouns ending in “-o”.
Potassium: Correct spelling; name of a chemical element, commonly used in science and health contexts.

Common Pitfalls:
Students sometimes rush and mark familiar-looking but correct words, such as “plaintiff” or “potatoes”, thinking they must contain a trick. Another trap is being misled by the sound “train” in “pedestrain”, which may seem familiar from words like “train” or “strain”. To avoid such errors, slow down and mentally spell each word syllable by syllable. For example: pe-des-tri-an, not pe-des-train. This habit strengthens your visual memory of correct spellings and improves your accuracy in spelling-based questions.

Final Answer:
Correct answer: pedestrain.