Explanation: The chemical name of baking powder is sodium bicarbonate (NaHCO₃), also known as baking soda. It is a mild alkali used in cooking and baking as a leavening agent. When heated or mixed with an acid (like vinegar, lemon juice, or cream of tartar), it decomposes to release carbon dioxide gas (CO₂). The bubbles of CO₂ make the dough rise and become soft and spongy. In commercial baking powder, sodium bicarbonate is often mixed with a weak acid and a drying agent.

Explanation: Natural gas is not a renewable source of energy because it is a fossil fuel formed over millions of years from the remains of plants and animals. Once used, it cannot be replenished quickly. In contrast, geothermal energy, flowing water, and biomass are renewable energy sources that can be naturally regenerated.

Explanation: The permissible noise level in residential areas should not exceed 55 decibels (dB) during the daytime and 45 dB at night, as per the Central Pollution Control Board (CPCB) guidelines. Exposure to higher noise levels can lead to stress, disturbed sleep, and hearing impairment.

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.

The Widal test is used to diagnose Typhoid fever, a bacterial infection caused by Salmonella typhi. The test detects the presence of agglutinating antibodies (O and H) in a patient’s serum against the antigens of the typhoid bacteria. It helps confirm infection during the second week of illness.

• Cholera: Diagnosed by stool culture for Vibrio cholerae.
• Tuberculosis: Detected using sputum test or Mantoux test.
• AIDS: Diagnosed through ELISA or Western blot test for HIV.

Explanation: Red light is used in traffic signals because it has the longest wavelength among all visible colors. Due to this property, it gets scattered the least and can travel the farthest through fog, rain, or dust, making it easily visible from a long distance and ideal for indicating ‘stop’.

Explanation: Plants absorb nitrogen from the soil mainly in the form of nitrates (NO₃⁻). Inside the plant, nitrates are reduced to nitrites (NO₂⁻) and then to ammonia (NH₃) through the action of specific reductase enzymes. The ammonia thus formed is then used to synthesize amino acids, proteins, nucleic acids, and other nitrogen-containing compounds necessary for plant growth.

Simplified Pathway:

NO₃⁻ → NO₂⁻ → NH₃ → Amino acids → Proteins

The Red Data Book contains information about endangered and threatened species of plants and animals. It is published by the International Union for Conservation of Nature (IUCN). The book categorizes species based on their risk of extinction, such as Critically Endangered, Endangered, Vulnerable, and Extinct. It serves as a global reference for monitoring biodiversity conservation and guiding environmental protection policies.

Other options (for context)

• All plant species: Incorrect — it includes only those plants that are endangered or threatened.
• All animal species: Incorrect — it covers only the endangered and vulnerable ones, not all animals.
• All extinct species: Incorrect — it includes species at risk of extinction, not only those already extinct.