Atomic number of sodium is 11. Its electronic configuration is: MCQ with Answer and Explanation

Explanation:
Silver and gold are noble metals and occur in the free (native) state in nature because they are extremely unreactive (least reactive), not highly reactive. They do not readily combine with oxygen, moisture, or acids. Thus, A is true, but R is false.

Explanation:
Hydrogen has about 141.9 kJ/g, the highest of any fuel. Methane ~55.5 kJ/g, coal ~25-35 kJ/g, wood ~17 kJ/g. Hydrogen produces only water on combustion, making it a clean fuel.

Explanation:
Graphite conducts electricity due to delocalized electrons in its structure and is chemically inert, allowing its use in electrodes for electrolysis and batteries. Diamond is an insulator. Hardness is not the reason; graphite is soft. It is opaque and black. Graphite electrodes are used in arc furnaces.