In October 2015, more than 350 landmarks in over 90 countries were lit blue to mark which United Nations occasion?

Introduction / Context:
The United Nations often organises global campaigns using its official colour blue to promote important milestones and international observances. In October twenty fifteen, a large number of famous landmarks around the world were illuminated in blue. Examinations may ask which anniversary or event this illumination was meant to celebrate, so this question tests your awareness of world organisations and special commemorations.

Given Data / Assumptions:

• The year mentioned is twenty fifteen.
• More than three hundred fifty landmarks in over ninety countries were lit blue.
• The options list various anniversaries of the United Nations.

Concept / Approach:
The United Nations was founded in nineteen forty five after the Second World War. Therefore, its significant anniversaries can be calculated from that year. The seventieth anniversary falls in twenty fifteen. The lighting of global landmarks in blue was part of the celebrations for seventy years of the organisation. Thus, by simple date calculation and recall of current affairs, you can pick the correct option.

Step by Step Solution:
Step 1: Start from the founding year of the United Nations, which is nineteen forty five. Step 2: Calculate the seventieth anniversary by adding seventy years to nineteen forty five, giving twenty fifteen. Step 3: Notice that the question mentions October twenty fifteen and a special blue lighting campaign. Step 4: Match this information with the known global campaign to light landmarks blue for the seventieth anniversary of the United Nations. Step 5: Therefore, the correct answer is the seventieth anniversary, not any of the other anniversaries listed.

Verification / Alternative check:
A quick check is to compute other anniversaries in the options. The fiftieth anniversary would have been in nineteen ninety five, the sixtieth in two thousand five, and the ninetieth in twenty thirty five. None of these match twenty fifteen. News reports and official United Nations releases from twenty fifteen highlight the blue illumination campaign using the slogan Turn the world UN blue to mark seventy years of the organisation, which confirms the correct choice.

Why Other Options Are Wrong:
Ninetieth anniversary of the United Nations: This would occur in twenty thirty five and is in the future relative to twenty fifteen, so it cannot be correct.
Fiftieth anniversary of the United Nations: This took place in nineteen ninety five, long before the events in twenty fifteen, so this option is incorrect.
Sixtieth anniversary of the United Nations: This would have been in two thousand five, again not matching the year of the blue lighting campaign.

Common Pitfalls:
Some students may not recall the founding year of the United Nations and might try to guess based on recent news. Another common error is to miscalculate the difference between nineteen forty five and twenty fifteen. To avoid mistakes, remember the founding year as a fixed fact and practise simple anniversary calculations, which frequently appear in general knowledge questions.

Final Answer:
The blue illumination campaign in October twenty fifteen marked the seventieth anniversary of the United Nations.