Chemistry

Neon is the gas most commonly used in neon signs because it emits a bright reddish-orange glow when an electric current passes through it. Other gases are used for different colors, but neon is the standard for the classic neon sign.

Helium is commonly used in balloons and airships because it is lighter than air and non-flammable, making it safer than hydrogen.

The chemical formula for water is H2O, which consists of two hydrogen atoms bonded to one oxygen atom. This is a fundamental fact in chemistry.

The modern Periodic Table consists of 7 rows called periods and 18 columns called groups. This arrangement reflects the recurring chemical properties of elements.

In the periodic table, columns are called groups. Each group contains elements with similar chemical properties due to their similar valence electron configurations.

In the periodic table, the horizontal rows are called periods. Each period corresponds to elements with the same number of electron shells.

Chlorine, Fluorine, and Iodine are all halogens, which are elements found in Group 17 of the periodic table. They share similar chemical properties, making option D the correct analogy.

Radium, Polonium, Uranium, and Thorium are all radioactive elements, making Thorium the correct choice as it shares this property with the others. Caesium, Barium, and Strontium are not all radioactive, so they do not fit the group as well.

Vulcanisation is a chemical process involving sulphur to harden rubber, similarly, chlorine is commonly used in the bleaching process. Hence, the analogy is correct with 'Bleaching' as the answer.

The term 'most stable element' can refer to different types of stability: chemical stability or nuclear stability. Chemically, hydrogen is quite stable due to its simple atomic structure, but it is highly reactive in many conditions. Uranium is radioactive and unstable. Oxygen is reactive. Lead, particularly the isotope lead-208, is known for its nuclear stability as it is one of the heaviest stable nuclei with a high binding energy per nucleon, making it very stable against radioactive decay. Therefore, among the options given, lead is considered the most stable element overall in terms of nuclear stability.