The correct answer is option 'A' - Haldia.

Haldia port is a major seaport located in West Bengal, India. It is situated on the banks of the Haldi River, hence the name "Haldia". The port was developed to relieve the pressure on Kolkata port, which was facing congestion and capacity constraints.

Here is an explanation of why Haldia port was developed to relieve the pressure on Kolkata port:

1. Congestion at Kolkata Port:
- Kolkata port, also known as Kolkata-Haldia port complex, is one of the oldest and busiest ports in India.
- Over the years, the port faced significant congestion due to increased trade activities and lack of sufficient infrastructure.
- The increasing volume of cargo and ships led to delays, longer turnaround times, and decreased efficiency at Kolkata port.

2. Need for Additional Port:
- To address the congestion and capacity constraints at Kolkata port, the development of an additional port became necessary.
- Haldia, which is located downstream of Kolkata on the Haldi River, was identified as a suitable location for the new port.

3. Development of Haldia Port:
- Haldia port was developed as a satellite port to Kolkata port, with the aim of diverting some of the traffic and cargo to relieve the pressure on Kolkata port.
- The construction of the port began in the 1960s, and it became operational in 1977.
- Haldia port has modern infrastructure, including deep-water berths, cargo handling facilities, and storage areas.
- The port is well-connected to the hinterland through road and rail networks, facilitating the movement of cargo.

4. Key Advantages of Haldia Port:
- Haldia port offers several advantages, which made it an ideal choice for relieving the pressure on Kolkata port.
- It has a draft that allows larger vessels to dock, reducing the congestion caused by smaller vessels at Kolkata port.
- The port has ample land for expansion and the potential to handle a significant volume of cargo.
- Haldia port is strategically located near industrial areas, including the Haldia Petrochemical Complex, which helps in the efficient movement of goods.

Conclusion:
In conclusion, Haldia port was developed to relieve the pressure on Kolkata port, which was facing congestion and capacity constraints. The construction of Haldia port provided an additional seaport with modern infrastructure, capable of handling a significant volume of cargo and accommodating larger vessels. This helped in improving the efficiency of trade and reducing congestion at Kolkata port.