Explanation

• Hydrogen and helium are the two lightest gases.
• Helium is the second most abundant element in the universe, after hydrogen.
• Helium has monatomic molecules.
• It is the lightest of all gases except hydrogen.
• Hydrogen is the lightest gas known.
• It provides the maximum lift for balloons due to its very low density.

Last updated question 17-02-2026

Explanation

• Carbon dioxide (CO₂) is used in fire extinguishers.
• It extinguishes fire by displacing oxygen and cooling the burning material.
• CO₂ fire extinguishers are especially effective for electrical and flammable liquid fires.
• Carbon dioxide is a colorless and non-flammable gas.
• It leaves no residue after use.

Explanation

• Mercury Symbol: Hg
• Atomic number: 80
• Melting point: -38.83 °C
• Atomic mass: 200.59 u

Last verified on 13-03-2026

Explanation

• Marie Curie is the only person to win Nobel Prizes in two different natural sciences.
• She won the Nobel Prize in Physics in 1903.
• She won the Nobel Prize in Chemistry in 1911.
• She was awarded for her pioneering work on radioactivity.

Last verified on 06-09-2026

Explanation

• Aldehydes give a silver mirror test with Tollens' reagent.
• Tollens' reagent contains the diamminesilver(I) ion, [Ag(NH₃)₂]⁺.
• The aldehyde is oxidized to a carboxylic acid/carboxylate, while Ag⁺ is reduced to metallic silver.
• The deposited silver forms a shiny silver mirror on the test tube.

Last verified on 05-09-2026