India has installed its tallest national flag calculated from the average elevation of the city in which of the following Indian cities?

Introduction / Context:
Current affairs based general knowledge often includes questions about record breaking structures like the tallest statues, largest dams or tallest national flags. In 2018 a very tall national flag measured from the average elevation of the city was installed in an important northeastern city. This question tests awareness of that event and requires recognition of the correct city.

Given Data / Assumptions:

• The record refers to India's tallest national flag from the average city elevation.
• Options include Guwahati, Bengaluru, Mumbai and Hyderabad.
• The flag referenced in news reports was installed on a tall flagpole at Gandhi Mandap in a hill city.
• We assume the question is about that specific record and not other tall flags at border areas.

Concept / Approach:
The phrase from the average city elevation is important. It distinguishes this record from flags at low lying border areas where height above ground is high but elevation above sea level is lower. News coverage highlighted Assam dedicating India's tallest national flag from average city elevation at Guwahati, located on hills above the Brahmaputra river. Remembering this fact from current affairs compilations allows us to pick the correct option.

Step-by-Step Solution:
Step 1: Recall that in October 2018 Assam unveiled a monumental national flag at Gandhi Mandap in Guwahati. Step 2: Reports described this flag as India's tallest national flag from the average elevation of the city, with a pole height of more than three hundred feet. Step 3: Bengaluru, Mumbai and Hyderabad are major metros but they were not associated in news with this particular phrasing about average city elevation. Step 4: Therefore the city that matches this record is Guwahati in Assam.

Verification / Alternative check:
A quick verification approach is to link states to these cities and recall relevant events. Mumbai in Maharashtra is known for the Gateway of India, stock exchange and coastal landmarks. Bengaluru in Karnataka is known for information technology and startups. Hyderabad in Telangana is associated with Charminar and biryani. Guwahati stands out in northeast India and the event of a very tall flag at Gandhi Mandap received specific coverage, often cited in exam oriented current affairs notes under Assam developments. This strengthens the identification of Guwahati as correct.

Why Other Options Are Wrong:
Option Bengaluru is wrong because although it is a high elevation city on the Deccan plateau, there was no widely reported record about the tallest national flag from average city elevation there at the time referenced. Option Mumbai is wrong since its major flags do not hold this particular record; Mumbai is at sea level and the city is not described with that elevation based wording. Option Hyderabad is wrong because its famous landmarks include Charminar, Golconda fort and high tech city, not this specific tallest flag record.

Common Pitfalls:
One common pitfall is to ignore the phrase from the average city elevation and simply recall any news about tall flags, which might include border locations like the Attari Wagah border. Those flags are tall but they are not linked with the given phrase. Another mistake is to guess based on city size and choose Mumbai or Bengaluru. Focusing on the exact wording used in newspapers and exam oriented magazines is crucial for handling such nuanced factual questions.

Final Answer:
India's tallest national flag measured from the average elevation of the city has been installed in Guwahati in Assam.