To complete the given city names' series logically, we need to identify the common characteristic shared by Darjeeling, Ooty, Manali, and Pahalgam. Once this pattern is recognized, we can find the option that consistently follows the same logic.

Series Pattern: Hill Stations of India

Let's analyze each city in the provided series:

• Darjeeling: This is a well-known hill station located in the Indian state of West Bengal, famous for its tea gardens and scenic beauty.
• Ooty: Officially known as Udhagamandalam, Ooty is a popular hill station in the Nilgiri Hills of Tamil Nadu, South India.
• Manali: Situated in the Beas River Valley, Manali is a very famous hill station in the Kullu District of Himachal Pradesh, known for its adventure tourism.
• Pahalgam: Located in the Anantnag district of Jammu and Kashmir, Pahalgam is a prominent hill station and a major tourist destination in the Himalayas.

From this analysis, it is clear that all the cities in the series—Darjeeling, Ooty, Manali, and Pahalgam—are prominent and popular hill stations across different parts of India.

Mussoorie: The Logical Continuation

Now, let's examine the given options to find the one that fits this established pattern of being a hill station:

• Pune: Pune is a major metropolitan city in the Indian state of Maharashtra, known as an educational and IT hub. It is not primarily a hill station.
• Jaipur: Jaipur is the capital and largest city of the Indian state of Rajasthan. It is known as the "Pink City" and is a major tourist destination for its historical palaces and forts, but it is not a hill station.
• Agra: Agra is a city in the Indian state of Uttar Pradesh, famous worldwide for the iconic Taj Mahal. It is a historical and cultural city, not a hill station.
• Mussoorie: Mussoorie is a famous hill station and a municipal board in the Dehradun District of Uttarakhand, India. It is often referred to as the "Queen of the Hills" due to its picturesque views and pleasant climate.

Based on the common characteristic of the series (Darjeeling, Ooty, Manali, Pahalgam) being popular hill stations, Mussoorie is the only option that logically completes the series, as it is also a prominent hill station in India.