Among the months MARCH, MAY, JUNE and DECEMBER, identify the odd one out based on the number of days.

Introduction / Context:
Calendar based odd one out questions are standard in verbal reasoning and general awareness sections. These questions rely on basic facts about months, such as the number of days in each month or their position in the year. In this problem, four month names are given, and we must select the one that differs from the others according to the number of days in that month.

Given Data / Assumptions:
The months given are March, May, June and December. We use the standard Gregorian calendar. March, May and December each have 31 days. June has 30 days.

Concept / Approach:
The key concept here is the distribution of 30 day and 31 day months in a year. March, May, July, August, October and December all have 31 days, while April, June, September and November have 30 days. February is special with 28 or 29 days. By checking each option against this rule, we can quickly see which month does not match the others in terms of day count. The month with 30 days among mostly 31 day months will be the odd one out.

Step-by-Step Solution:
Step 1: March is a 31 day month. Step 2: May is a 31 day month. Step 3: December is also a 31 day month. Step 4: June is a 30 day month, which is different from the others listed. Step 5: Since three of the months have 31 days and one month has 30 days, that one month is the odd one out. So June is the answer.

Verification / Alternative check:
You can recollect the common mnemonic knuckle rule or the rhyme used to remember the day count of each month. In every version of this memory aid, June consistently appears as a 30 day month. March, May and December are always confirmed as 31 day months. Because this is a fixed feature of the calendar, there is no ambiguity in the classification.

Why Other Options Are Wrong:
March is not the odd one out because its 31 day count matches that of May and December. May is not the odd one out because it also has 31 days and belongs to the same group as March and December. December is not the odd one out because it too has 31 days. Only June differs because it has 30 days, making it the odd one.

Common Pitfalls:
Some candidates focus on the position in the year, such as thinking December is different because it is the last month, forgetting that the question is about a more basic property. Others may confuse months with 30 and 31 days if they have not revised the calendar properly. Reviewing the months and their day counts before exams helps avoid simple but costly mistakes in such questions.

Final Answer:
The only month among the options that has 30 days and is therefore the odd one out is JUNE.