Shivanasamudra and Kalpakkam are respectively important for:

1. A

   Hydel Power and Nuclear Energy

   This option claims that Shivanasamudra is important for Hydel Power and Kalpakkam is important for Nuclear Energy. Shivanasamudra, located on the Kaveri River in Karnataka, houses one of the earliest hydro-electric power stations in Asia established in 1902. Kalpakkam in Tamil Nadu is well-known for hosting the Madras Atomic Power Station and the Indira Gandhi Centre for Atomic Research. Since both associations are geographically and historically accurate, this option correctly identifies the primary significance of both locations and serves as the correct key.

2. B

   Thermal Power and Nuclear Energy

   This option claims that Shivanasamudra is important for Thermal Power and Kalpakkam is important for Nuclear Energy. While Kalpakkam is indeed associated with nuclear energy, Shivanasamudra is famous for hydroelectricity rather than thermal power generation. Therefore, attributing thermal power generation to Shivanasamudra makes this option incorrect.

3. C

   Nuclear Energy and Hydel Power

   This option claims that Shivanasamudra is important for Nuclear Energy and Kalpakkam is important for Hydel Power. This reverses the energy sectors associated with both locations completely. Kalpakkam is a prominent nuclear facility, and Shivanasamudra is a historic hydel power station, making this choice entirely wrong.

4. D

   Solar Power and Nuclear Energy

   This option claims that Shivanasamudra is important for Solar Power and Kalpakkam is important for Nuclear Energy. Although Kalpakkam is correctly matched with nuclear energy, Shivanasamudra is not primarily recognized as a major solar power center in Indian energy history. Consequently, this incorrect classification of Shivanasamudra eliminates this choice.

Summary. Official key is (a) Hydel Power and Nuclear Energy. Shivanasamudra is historically famous as one of India's earliest hydro-electric power stations situated on the Kaveri River. Kalpakkam is renowned for its major nuclear power installations and research centers in Tamil Nadu. Candidates must carefully distinguish between the hydro-electric legacy of Shivanasamudra and atomic energy hubs like Kalpakkam. Therefore, option (a) is the only choice that accurately pairs both locations with their correct energy sectors.