Everyday Science

Stainless steel is an alloy of iron, chromium, and other elements that does not contain copper. Other options like brass (copper+zinc), bronze (copper+tin), and German silver (copper+nickel+zinc) all contain copper.

The cetane number is used to rate diesel oil, indicating its combustion quality. Higher cetane numbers mean better ignition quality and smoother combustion in diesel engines, similar to how octane rating works for petrol.

Bleaching powder (calcium hypochlorite) is obtained by the interaction of chlorine with a dilute solution of calcium hydroxide (slaked lime). The reaction produces Ca(OCl)Cl which acts as the bleaching agent.

Nitrogen is required by plants in the largest quantity among these options. It's essential for chlorophyll production, protein synthesis, and overall plant growth. Plants absorb nitrogen primarily as nitrates or ammonium from soil.

Ammonia (NH3) is widely used in refrigeration systems due to its excellent thermodynamic properties, high heat transfer efficiency, and zero ozone depletion potential. It's commonly used in industrial refrigeration and cold storage.

Citric acid is naturally found in citrus fruits like lemons, oranges, and limes. It gives these fruits their characteristic sour taste and is widely used as a food preservative and flavoring agent. Lactic acid is found in milk, tartaric acid in grapes, and acetic acid in vinegar.

Duralumin is a strong, lightweight alloy composed primarily of aluminium (about 95%), with copper (about 4%), magnesium (about 0.5%), and manganese. It was developed for aircraft construction and other applications requiring high strength-to-weight ratio. Bronze contains copper and tin, magnalium is aluminium-magnesium, and monel is nickel-copper.

Nickel is the catalyst used in the hydrogenation of vegetable oils to convert unsaturated fats into saturated fats, producing solid fats like margarine and vegetable ghee. The process involves adding hydrogen gas to the double bonds of unsaturated fatty acids. Nickel's catalytic surface facilitates this reaction at high temperatures and pressures.

Polycarbonates are tough, transparent thermoplastics with excellent impact resistance, making them ideal for bullet-proof glass, security windows, and protective gear. Their molecular structure contains carbonate groups that provide exceptional strength. Polyvinyl chloride is used for pipes, polyamides (nylon) for textiles, and polyethylene for packaging.

The human body is primarily composed of oxygen (about 65%), carbon (about 18.5%), hydrogen (about 9.5%), nitrogen (about 3.2%), calcium (about 1.5%), and phosphorus (about 1.0%). Iron, while essential for hemoglobin, constitutes only about 0.006% of body mass, making it the least abundant among these options.

Oxygen is the most abundant element in the Earth's crust, constituting approximately 46.6% by weight. It's found in silicate minerals, oxides, and water. Silicon is the second most abundant (about 27.7%), followed by aluminum (about 8.1%), and iron (about 5.0%). Carbon, hydrogen, and nitrogen are much less abundant in the crust.

LPG (Liquefied Petroleum Gas) is naturally odorless, so sulfur-containing compounds like ethyl mercaptan (ethanethiol) or thiophane are added as odorants to make leaks detectable. These compounds have an extremely strong smell detectable at very low concentrations (as low as 1 part per billion). The sulfur in these compounds produces the characteristic 'rotten egg' smell.

Cobalt oxide (specifically cobalt(II) oxide, CoO) has been used for centuries as a coloring agent to produce deep blue glass and ceramics known as 'cobalt blue.' The cobalt ions in the glass matrix absorb light in the red and yellow regions of the spectrum, transmitting blue light. Iron oxide gives colors from yellow to red, while nickel produces green to brown tints.

Unripe fruits contain high concentrations of organic acids such as citric acid, malic acid, and oxalic acid. As fruits ripen, these acids are metabolized or converted to sugars, reducing the sour taste. This is why unripe fruits taste sharp or bitter while ripe ones taste sweet. Starch, carotenoids, and lipids don't produce this characteristic sour taste.

Chromium has an atomic weight of approximately 52, while iron has an atomic weight of approximately 56. The other metals listed all have higher atomic weights: nickel (59), zinc (65), and copper (~64). This question tests knowledge of relative atomic masses in the periodic table, with chromium being the lightest among the options.

Mercury is the only metal that exists as a liquid at standard temperature and pressure (room temperature). It has a melting point of -38.83°C and a boiling point of 356.73°C. This unique property is due to mercury's weak metallic bonding from its filled 4f subshell and relativistic effects that stabilize the 6s electrons. All other metals listed are solids at room temperature.

DDT (Dichlorodiphenyltrichloroethane) is a synthetic insecticide that was widely used to control mosquitoes and other disease-carrying insects. It works by disrupting sodium ion transport in nerve cells, leading to paralysis and death. Herbicides kill weeds, fungicides kill fungi, and rodenticides kill rodents. DDT's use is now restricted due to environmental concerns.

Urea (CO(NH2)2) contains approximately 46% nitrogen by mass, which is the highest among all common nitrogen fertilizers. Calcium ammonium nitrate contains about 27-28% nitrogen, ammonium sulphate contains 21%, and calcium nitrate contains about 15-17%. The high nitrogen content makes urea an efficient and economical choice for farmers.

Dmitri Ivanovich Mendeleev is credited with developing the Periodic Law in 1869, which states that chemical properties of elements are a periodic function of their atomic masses. He created the first periodic table and even predicted the existence and properties of elements that had not yet been discovered. Niels Bohr developed atomic structure theory, Huygens studied wave optics, and Newton formulated classical mechanics.

CFCs (Chlorofluorocarbons) were widely used as refrigerants in refrigerators and air conditioning systems, and as propellants in aerosol sprays. However, they were never used in fire extinguishers - fire extinguishers typically use carbon dioxide, foam, dry chemical powders, or halon (before its phase-out). CFCs were phased out globally under the Montreal Protocol due to their ozone-depleting properties.

Acetylene gas (C2H2) is commonly used for artificial ripening of fruits, especially in developing countries. It acts similarly to ethylene (the natural ripening hormone in fruits). While ethylene is the preferred industrial ripening agent worldwide, acetylene is cheaper and more accessible. The other gases listed (ethane, hydrogen, CO2) do not stimulate fruit ripening.

Ammonium nitrate (NH4NO3) mixed with diesel fuel or other fuel oil creates ANFO (Ammonium Nitrate Fuel Oil), a powerful explosive commonly used in mining and construction. Unfortunately, this combination has also been used in terrorist attacks due to the easy availability of ammonium nitrate as fertilizer. Semtex, C-4, and TNT are already explosive compounds and do not need to be mixed with fuel to become destructive.