The setting time of cement is controlled by adding: MCQ with Answer and Explanation

Explanation:
Refining is the final step in metallurgy to obtain pure metal. Poling is used for copper to remove oxide impurities. Liquation separates low-melting metals (like tin) from high-melting impurities. Zone refining is used for producing ultra-pure semiconductors (like Si, Ge) based on the principle that impurities are more soluble in the molten state.

Explanation:
Half-life is a characteristic of first-order kinetics, and all radioactive decay follows first-order kinetics. Hence it applies to all radioactive decay processes. Chemical reactions of first order also have constant half-life independent of initial concentration, but radioactive decay is the prime example. Zero-order half-life depends on initial concentration.

Explanation:
Starch (polysaccharide) is a natural polymer made from glucose units. It is found in plants. Cellulose, proteins, natural rubber are natural polymers. PVC, nylon, Teflon are synthetic polymers. Natural polymers are biodegradable and renewable. Starch is used as food, in paper, and bioplastics. Synthetic polymers are often derived from petrochemicals.