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

Explanation:
The quantum numbers n=3 and l=1 specify the 3p subshell. The magnetic quantum number m=-1 specifies one particular 3p orbital within that subshell. According to Pauli's Exclusion Principle, a single orbital can accommodate a maximum of two electrons, which must have opposite spins (+1/2 and -1/2).

Explanation:
A molecule is a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction while retaining the composition and chemical properties of that substance. For example, H₂O molecule shows properties of water. Atoms (like He) can also be independent, but a molecule of an element (O₂) or compound retains identity.

Explanation:
Magnesium oxide (MgO) is an ionic compound. Magnesium (2,8,2) loses two electrons to become Mg²⁺, and oxygen (2,6) gains two electrons to become O²⁻. This electron transfer forms an electrovalent (ionic) bond. Covalent bonds involve sharing (e.g., H₂O).