The relationship between focal length (f) and radius of curvature (R) is: R = 2f. Therefore, R = 2 × 20 = 40 cm.

Melting of ice is an endothermic process as it requires heat energy input to convert solid ice into liquid water. Other options are exothermic reactions that release heat.

The pH scale ranges from 0 to 14, where 7 is neutral, below 7 is acidic, and above 7 is basic/alkaline.

Gravitational potential energy = mgh = 5 × 10 × 2 = 100 J

Insulin, produced by the pancreas, regulates blood glucose levels by promoting glucose uptake by cells.

Newton's third law states that for every action, there is an equal and opposite reaction. This means forces always act in pairs - if object A exerts a force on object B, then B exerts an equal force on A in the opposite direction.

The kidneys are bean-shaped organs that filter waste products and excess water from the blood to produce urine. A human typically has two kidneys.

Methane (CH₄) is the main component of natural gas, comprising about 70-90% of its composition. It is the simplest hydrocarbon and is widely used as a fuel.

Melting of ice is an endothermic reaction as it requires absorption of heat energy. Combustion and rusting are exothermic reactions that release heat; condensation is also exothermic.

Photosynthesis is the process by which plants convert light energy into chemical energy in the form of glucose, using carbon dioxide and water. The overall equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.