The hardest natural substance known is: MCQ with Answer and Explanation

Explanation:
Group 18 elements are noble gases: helium, neon, argon, krypton, xenon, radon. They have completely filled valence shells, making them chemically inert (though xenon can form compounds). Nitrogen is Group 15, Oxygen Group 16, Hydrogen is unique (Group 1).

Explanation:
N₂ has a triple bond (N≡N), consisting of one sigma and two pi bonds. This is the strongest type of covalent bond, giving N₂ high stability and low reactivity. Bond order is 3. The molecule is diatomic and nonpolar.

Explanation:
The reactivity series arranges metals from most reactive (K) to least reactive (Au). A metal higher in the series can displace a lower one from its salt solution. The order is based on tendency to lose electrons (form positive ions). More reactive = more electropositive.