Everyday Science

In soap manufacture, oils (fats) react with sodium hydroxide to produce soap and glycerine as a by-product. Therefore, glycerine is obtained during the process.

Lemons are sour because they contain citric acid, which gives them their characteristic tart taste. The other acids listed are found in different substances and do not primarily cause the sourness in lemons.

Oxygen is essential for burning because it supports the chemical reaction of combustion. Without oxygen, burning cannot occur.

Specific gravity is a ratio of the density of a substance to the density of a reference substance (usually water), making it a dimensionless quantity with no units.

Oil rises in the wick of an oil lamp due to capillary action, which is the ability of a liquid to flow in narrow spaces without external forces, caused by adhesion and cohesion.

Atmospheric pressure decreases rapidly with altitude because the air becomes less dense as altitude increases, resulting in fewer air molecules exerting pressure.

Onion seeds are typically rectangular in shape, unlike the other options whose seeds are round or differently shaped. Therefore, the vegetable crop with rectangular seeds is Onion.

The frequency of a tuning fork is determined using a sonometer, which measures the frequency of vibrating strings and can be used to compare with the tuning fork's frequency.

Atmospheric pressure at sea level is standardly defined as 760 mm of mercury (mmHg). This is the commonly accepted value for atmospheric pressure under normal conditions.

Football is a high-intensity sport involving continuous running and physical exertion, leading to the highest calorie consumption among the options listed. Cricket, golf, and billiards involve less intense physical activity and thus burn fewer calories.