The half-life of a radioactive isotope is 10 years. What fraction of the original sample will remain after 30 years? MCQ with Answer and Explanation

Explanation:
In an oxygen molecule (O₂), each oxygen atom has 6 valence electrons and needs 2 more to complete its octet. They share two pairs of electrons, forming a double covalent bond (O=O). H₂ and Cl₂ have single bonds, while N₂ has a triple covalent bond (N≡N).

Explanation:
Cement undergoes hydration reactions: water reacts with cement compounds (C₃S, C₂S, C₃A) to form complex hydrated silicates and aluminates (e.g., C-S-H gel) along with Ca(OH)₂. This process causes setting and hardening, forming a rigid, rock-like mass. It is exothermic. Gypsum controls initial setting. Proper curing is necessary for strength development.

Explanation:
In diamond, each carbon atom is sp³ hybridized and forms four strong covalent bonds, utilizing all four valence electrons. No free electrons are available for conduction. Graphite has free delocalized electrons per carbon, making it a conductor.