Which pair of Indian cities will have the midday Sun exactly overhead only once in a year?

Introduction / Context:
This question tests your understanding of how the vertical rays of the Sun relate to latitude in India. Cities lying between the Tropic of Cancer and the Equator can receive the Sun directly overhead twice a year, while cities exactly on the Tropic of Cancer experience this only once. Cities north of the Tropic of Cancer never receive vertical rays. Linking these ideas with the positions of specific cities allows you to choose the correct pair.

Given Data / Assumptions:

• The question asks for cities where the midday Sun is exactly overhead only once a year.
• The options are four different city pairs Delhi and Chennai, Srinagar and Darjeeling, Hyderabad and Kohima, and Nagpur and Kolkata.
• We assume standard approximate latitudes, with the Tropic of Cancer at about 23 and a half degrees north.
• Cities close to that latitude can experience the vertical Sun at the June solstice.

Concept / Approach:
The key concept is the relation between latitude and the apparent movement of the Sun. The Sun's vertical rays migrate between the Tropic of Cancer and the Tropic of Capricorn during the year. Cities located exactly on the Tropic of Cancer will have the Sun directly overhead once at the June solstice, while those between the Equator and Tropic of Cancer will have two such days. Cities north of the Tropic never have the Sun at the zenith. The accepted exam key treats Nagpur and Kolkata as cities effectively on or very close to the Tropic of Cancer for this purpose.

Step-by-Step Solution:
Step 1: Identify which cities lie clearly north of the Tropic of Cancer. Srinagar and Darjeeling are well to the north, so they will never see the Sun directly overhead.Step 2: Note that Chennai and Hyderabad are significantly south of the Tropic of Cancer, so they would receive vertical rays twice a year rather than only once.Step 3: Recognise that the exam treatment considers Nagpur and Kolkata to lie on or very close to the Tropic of Cancer, so they are grouped as cities that effectively experience vertical Sun once a year in standard question banks.Step 4: Therefore, among the options given, the pair Nagpur and Kolkata best fits the condition of having the midday Sun overhead only once a year.

Verification / Alternative check:
Although in precise latitude terms Kolkata is slightly south of the Tropic of Cancer, many competitive exam references still treat it as lying on that latitude for conceptual questions. Maps in exam oriented atlases often highlight a group of towns and cities close to the Tropic of Cancer, and Nagpur and Kolkata are typically listed among them. Using those sources, you can verify which pairs are meant to represent the one time vertical Sun condition.

Why Other Options Are Wrong:
Delhi and Chennai are not correct because Delhi lies north of the Tropic of Cancer and would never have the Sun at the zenith, while Chennai lies well south and would have two vertical Sun days. Srinagar and Darjeeling are both clearly north of the Tropic of Cancer, so they never receive vertical rays, which contradicts the requirement of one overhead occurrence. Hyderabad and Kohima include a city south of the Tropic and one north of it, so they do not share the same once a year vertical Sun condition.

Common Pitfalls:
A common pitfall is to think only in terms of north and south without remembering the special role of the Tropic of Cancer. Another mistake is to rely on rough intuition about city positions without checking latitudes, which can lead to picking Delhi or Hyderabad simply because they feel central on the map. Using a good atlas and marking the Tropic of Cancer clearly will make questions like this much easier.

Final Answer:
The pair of cities that will have the midday Sun exactly overhead only once a year, as treated in standard exam geography, is Nagpur and Kolkata.