The glacier of the Nubra Valley in the eastern Karakoram, the longest one with a length of over 72 kilometres, is known by which name?

Introduction / Context:
High mountain glaciers are important physical features in Indian and South Asian geography. Nubra Valley in the eastern Karakoram range is particularly known for a very long glacier that also has strategic significance. This question tests recognition of the name of that glacier based on its location and length.

Given Data / Assumptions:
• The glacier is located in the Nubra Valley in the eastern Karakoram. • It is described as the longest one in that context with a length of over 72 kilometres. • Options include Hispar, Siachen, Biafo, Baltoro and Zemu glaciers. • Standard Himalayan and Karakoram geography is assumed.

Concept / Approach:
Siachen Glacier is located in the eastern Karakoram range close to the Nubra Valley and is one of the longest glaciers in the world outside polar regions. It is well known in both geography and defence discussions, making it a frequent exam topic. The approach is to match the location Nubra Valley and the given length detail with the correct glacier name.

Step-by-Step Solution:
Step 1: Recall that Siachen Glacier lies in the eastern Karakoram, near the famous Siachen conflict zone and the Nubra Valley. Step 2: Its length is often quoted as more than 70 kilometres, which matches the description in the question. Step 3: The other glaciers listed such as Hispar, Biafo and Baltoro are primarily situated in the Karakoram region of present day Pakistan. Step 4: Zemu Glacier lies in the eastern Himalayas near Kangchenjunga, not in Nubra Valley. Step 5: Therefore Siachen Glacier is the correct answer.

Verification / Alternative check:
Physical geography and defence studies texts label Siachen Glacier as lying in Nubra Valley region of Ladakh and identify it as the longest glacier in that sector. Maps of the Karakoram show Siachen stretching for more than 70 kilometres along the high altitude valley. The other named glaciers are in different valleys or ranges and do not fit the Nubra location plus length combination.

Why Other Options Are Wrong:
Hispar Glacier: A large glacier in the Karakoram but not associated specifically with Nubra Valley. Biafo Glacier: Also a major glacier in the Karakoram region on the Pakistan side, not in Nubra Valley. Baltoro Glacier: A famous glacier near K2 in the Karakoram, again not the one described in the question. Zemu Glacier: Located in Sikkim near Kangchenjunga in the eastern Himalayas, far away from Nubra Valley.

Common Pitfalls:
Because many of these glaciers are in the broader Karakoram region, learners may confuse their locations and choose Baltoro or Biafo by mistake. Another pitfall is mixing up Nubra Valley in Ladakh with valleys in Pakistan controlled parts of the Karakoram. Remembering that Siachen Glacier is the long glacier located in the Nubra region on the Indian side helps anchor the correct answer.

Final Answer:
The longest glacier in Nubra Valley with a length of over 72 kilometres is the Siachen Glacier.