Explanation: Cobalt-60 (Co-60) is a radioactive isotope of cobalt that emits high-energy gamma rays during its decay process. It decays into Nickel-60 (Ni-60) by beta decay, releasing two strong gamma photons of energies 1.17 MeV and 1.33 MeV. Due to these intense gamma emissions, Co-60 is widely used in radiation therapy (teletherapy) for cancer treatment, as well as in industrial radiography and sterilization of medical equipment. Gamma rays have high penetration power, allowing them to destroy cancerous cells deep inside tissues.

Explanation: In humans, the spinal cord gives rise to 31 pairs of spinal nerves. Each spinal nerve is a mixed nerve containing both sensory and motor fibers. They are divided into groups based on the region of the vertebral column from which they originate:

• 8 pairs — Cervical nerves
• 12 pairs — Thoracic nerves
• 5 pairs — Lumbar nerves
• 5 pairs — Sacral nerves
• 1 pair — Coccygeal nerve

These spinal nerves connect the central nervous system (CNS) to different parts of the body, transmitting sensory information to the brain and motor commands to muscles.

Explanation: Dengue fever is caused by the Dengue virus, which belongs to the Flavivirus group. It is transmitted to humans through the bite of an infected Aedes aegypti mosquito. The virus multiplies in the blood and causes symptoms such as high fever, severe headache, joint and muscle pain, rashes, and low platelet count. In severe cases, it can lead to Dengue hemorrhagic fever or Dengue shock syndrome. Prevention includes controlling mosquito breeding and avoiding mosquito bites.

Explanation: The full form of USB is Universal Serial Bus. It is a standard interface used to connect devices such as keyboards, mice, flash drives, and printers to a computer. USB allows data transfer and power supply between connected devices.

Explanation: Uranium-235 (U-235) is the isotope used for the production of atomic energy because it is fissionable. When bombarded with neutrons, U-235 undergoes nuclear fission, releasing a large amount of energy along with additional neutrons, which sustain the chain reaction in nuclear reactors and atomic bombs.

The Air Quality Index (AQI) is a numerical scale used to measure and report the quality of air in a particular area. It primarily indicates the level of air pollution and its potential impact on human health. The AQI is calculated based on concentrations of key air pollutants — including ozone (O₃), particulate matter (PM₂.₅ and PM₁₀), nitrogen dioxide (NO₂), sulphur dioxide (SO₂), and carbon monoxide (CO). Higher AQI values indicate poorer air quality and greater health risks.

Other options (for context)

Running water is the source of hydel power (also called hydroelectric power). The energy of flowing or falling water is converted into electrical energy using turbines and generators in dams. It is a renewable, clean, and sustainable source of energy widely used in India and worldwide.

• Thermal power: Generated by burning coal or other fuels.
• Nuclear power: Produced from nuclear fission reactions.
• None of the above: Incorrect — running water directly produces hydel power.

Explanation: ASTROSAT is India’s first dedicated multi-wavelength space observatory launched by ISRO (Indian Space Research Organisation) on September 28, 2015. It is designed for astronomy research and studies celestial objects like stars, galaxies, black holes, and neutron stars in different wavelengths — including visible, ultraviolet, and X-ray bands. ASTROSAT helps scientists study high-energy astrophysical phenomena and provides data comparable to international missions such as NASA’s Hubble Space Telescope.