Sodium hydroxide is manufactured by: MCQ with Answer and Explanation

Explanation:
Number of half-lives = 24/8 = 3. Fraction remaining = (1/2)³ = 1/8. Activity = 100 × 1/8 = 12.5 counts per minute. Radioactive decay is exponential. After 1 half-life: 50, 2: 25, 3: 12.5. This isotope is used in thyroid treatment.

Explanation:
NPK stands for Nitrogen (N), Phosphorus (P, as P₂O₅), and Potassium (K, as K₂O). These are primary macronutrients essential for plant growth. The numbers on a fertiliser bag (e.g., 10-26-26) indicate the percentage of N, P₂O₅, and K₂O.

Explanation:
BOD stands for Biological Oxygen Demand. It is a measure of the amount of dissolved oxygen required by microorganisms to decompose the organic matter present in a water sample. High BOD indicates severe organic pollution and poor water quality for aquatic life.