Aryabhatta was a renowned mathematician and astronomer of ancient India. He lived during the Gupta period (around 476–550 CE) and authored the famous work Aryabhatiya. Aryabhatta introduced the concept of zero (0) and explained the place value system. He also proposed that the Earth rotates on its axis and correctly explained solar and lunar eclipses.

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• Doctor: No historical evidence of Aryabhatta being a physician.
• Poet: Although his works were written in verse form, his main field was mathematics and astronomy.
• Physicist: The term did not exist in his time; however, his scientific thinking laid foundations for later studies.

Explanation: Execution time is the period during which a job or program is actively processed by the computer’s CPU. It refers to the actual time taken to execute instructions, excluding waiting or idle times such as input/output delays or queue time.

Explanation: The ozone layer is located in the stratosphere, which is the second layer of the Earth’s atmosphere, lying above the troposphere and extending from about 10 km to 50 km above the Earth’s surface. The ozone layer contains a high concentration of ozone gas (O₃), which absorbs most of the Sun’s harmful ultraviolet (UV) radiation. This protective shield prevents genetic damage, skin cancer, and other harmful effects on living organisms.

Metals can be beaten into thin sheets because they are malleable. Malleability is a physical property of metals that allows them to withstand hammering or rolling without breaking. This property is due to the metallic bonding where positive metal ions are surrounded by a ‘sea’ of delocalized electrons, allowing the layers of atoms to slide over each other without breaking the bond. Examples of highly malleable metals include gold, silver, and aluminium.

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• Ductile: Refers to the ability of metals to be drawn into wires, not beaten into sheets.
• Soft: Not true for all metals — many are hard yet malleable.
• Loosely arranged particles: Incorrect — metal atoms are closely packed in a lattice structure.

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.

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Explanation: The Montreal Protocol, signed in 1987, is an international agreement aimed at protecting the ozone layer by phasing out the production and use of ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs) and halons. It is one of the most successful environmental treaties in history.

Ocean Thermal Energy (OTE) is produced due to the temperature difference at different levels in the ocean. The surface water is warmer because it absorbs sunlight, while the deeper layers remain cold. This temperature gradient is used to run a heat engine that generates electricity — a process known as Ocean Thermal Energy Conversion (OTEC).

• Tides: Related to gravitational pull, not temperature.
• Pressure difference: Exists but not used for energy generation.
• Waves: Used in wave energy systems, not OTEC.