Q1: The lightest non-inflammable gas is

ANS:B - He

Helium (He) is a chemical element with atomic number 2, making it the second lightest element in the periodic table after hydrogen. Here's an explanation of some key properties and characteristics of helium:

1. Chemical Symbol and Atomic Number: Helium is represented by the chemical symbol "He" and has an atomic number of 2, indicating that its nucleus contains two protons.
2. Abundance: Helium is one of the most abundant elements in the universe, although it is relatively rare on Earth's surface. It is primarily produced through nuclear fusion in stars, particularly during the process of hydrogen burning in the cores of stars like the Sun.
3. Physical Properties: Helium is a colorless, odorless, and tasteless gas at room temperature and pressure. It exists as a monatomic gas, meaning its molecules consist of individual helium atoms (He). Helium has the lowest boiling and melting points of any element, making it one of the few substances that remain liquid near absolute zero temperature.
4. Inertness: Helium is chemically inert under normal conditions, meaning it does not readily react with other elements or compounds. It is classified as a noble gas or inert gas due to its stable electronic configuration, with a full outer electron shell.
5. Non-Flammability: Helium is non-flammable and does not support combustion. This property makes it a safe choice for various applications where a non-reactive gas is required, such as in airships, balloons, and as a shielding gas in welding processes.
6. Applications: Helium has numerous practical applications, including:
   • Filling balloons and airships due to its low density and non-flammability.
   • Cooling superconducting magnets in MRI machines and particle accelerators due to its low boiling point.
   • Providing an inert atmosphere in controlled environments such as laboratories and semiconductor manufacturing.
   • Gas chromatography and leak detection due to its low reactivity and small atomic size.

Overall, helium is a fascinating element with unique properties that make it invaluable for various scientific, industrial, and commercial applications. Its combination of non-flammability, inertness, and low density makes it particularly useful in situations where safety and stability are paramount.