Explanation: Below the critical temperature, gases can be liquefied by applying pressure because the intermolecular forces of attraction between gas molecules become effective. These forces pull the molecules closer together, resulting in the formation of a liquid state.

Explanation: The sour taste of a lemon is due to the presence of citric acid. Citric acid is a weak organic acid found naturally in citrus fruits such as lemons, oranges, and limes. It gives them their characteristic tangy flavor and also acts as a natural preservative.

Explanation: The HIV (Human Immunodeficiency Virus) primarily attacks the lymphocytes, especially the CD4⁺ T-helper cells of the immune system. This weakens the body’s defense mechanism, making it vulnerable to various infections and diseases, eventually leading to AIDS (Acquired Immunodeficiency Syndrome).

Explanation: Vitamins are classified into two categories based on their solubility — fat-soluble and water-soluble. Vitamin C (ascorbic acid) and the B-complex vitamins are water-soluble, meaning they dissolve in water and are not stored in the body. Therefore, they must be consumed regularly through diet. Deficiency of Vitamin C causes scurvy, characterized by bleeding gums and delayed wound healing.

Explanation: The scientific name of Vitamin C is Ascorbic Acid. It is a water-soluble vitamin essential for the growth, repair, and maintenance of body tissues. Vitamin C acts as a powerful antioxidant and helps in the synthesis of collagen, absorption of iron, and boosting the immune system. A deficiency of Vitamin C leads to the disease Scurvy, characterized by bleeding gums, weakness, and delayed wound healing. Natural sources include citrus fruits like oranges, lemons, amla, and guava.

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: A mirage is an optical illusion caused by both refraction and total internal reflection of light. It occurs when light rays bend due to temperature variations in air layers near the ground, creating the illusion of water or a reflected image on hot surfaces like roads or deserts.

Explanation: Web pages are written using HTML (HyperText Markup Language). It is the standard language used to create and structure content on the web by defining elements such as headings, paragraphs, links, images, and tables.

Explanation: Chikungunya is a viral disease caused by the Chikungunya virus, which belongs to the Togaviridae family. It is transmitted to humans through the bite of infected Aedes aegypti and Aedes albopictus mosquitoes. The disease causes sudden fever, joint pain, headache, and rash. In contrast, cholera (caused by Vibrio cholerae), typhoid (by Salmonella typhi), and tuberculosis (by Mycobacterium tuberculosis) are all bacterial diseases.