Which of the following is a radioactive isotope used in the treatment of cancer? MCQ with Answer and Explanation

Explanation:
Across a period, nuclear charge increases while electrons are added to the same shell, leading to stronger attraction, so atomic radius decreases and ionization energy generally increases (with some exceptions like N to O due to half-filled stability). Metallic character decreases, non-metallic character increases. Electron affinity becomes more negative (increases in magnitude). Exam note: Ionization energy trend: Increases across period, decreases down group.

Explanation:
Biogas is produced from anaerobic digestion of organic waste (cow dung, agricultural residue) and is renewable. Mainly methane and CO₂. Coal, petroleum, and natural gas are fossil fuels formed over millions of years, non-renewable. Biogas plants generate clean fuel and also produce enriched manure. Charcoal is also not a fossil fuel; it's from wood pyrolysis.

Explanation:
Rigid PVC (unplasticized, uPVC) is hard, strong, and resistant to chemicals and weathering, making it ideal for pipes, window frames, and fittings. Flexible PVC uses plasticizers. It is not biodegradable. Transparency depends on additives; generally it's translucent. Its chemical resistance is due to the chlorine content.