Chemistry: Inorganic Chemistry: UPSC Previous Year Questions (Science and Technology)

Explanation

Option (b) is correct: Rubies and sapphires are both varieties of the mineral corundum, which is chemically known as aluminium oxide (Al₂O₃). The difference between rubies and sapphires lies in the trace elements present in them. Rubies get their red color from the presence of trace amounts of chromium. Sapphires can come in various colors, but they are typically blue due to trace amounts of iron and titanium. Options (a), (c) and (d) are incorrect:

Silicon dioxide (SiO₂) is the chemical compound for quartz, Lead tetroxide (Pb₄O₆) is a compound containing lead and oxygen and Boron nitride (BN) is a compound of boron and nitrogen. All three are not related to rubies or sapphires.

Explanation

Option (c) is correct: Xenon: Approximately 0.0000087% of Earth’s atmosphere, known as "stranger gas" due to its unusual behavior among noble gases. Unlike other noble gases, xenon can form compounds with other elements, such as xenon fluorides. It is used in high-intensity discharge lamps and flash lamps for bright illumination, explored as an anesthetic agent and in imaging techniques for the brain, heart, and lungs, and utilized in ion propulsion systems for satellites, contributing to efficient space travel. Options (a), (b) and (d) are incorrect:

Argon (Ar): Approximately 0.934% of Earth’s atmosphere, used in welding to create an inert atmosphere, in incandescent and fluorescent light bulbs to protect filaments from oxidation, and has potential as a neuroprotectant in medical applications. Neon: Neon (Ne) makes up about 0.0018% of Earth’s atmosphere. It is known for its use in neon signs that emit a reddish-orange glow. Neon is also used in lasers with helium to create specific light wavelengths. It helps detect leaks by identifying trace gases and is used as a cryogenic material for preserving biological specimens. Nitrous Oxide: Nitrous Oxide (N₂O), also called laughing gas, is colorless, odorless, and non-flammable. It has anesthetic properties and is used for minor surgeries and dental procedures. In the culinary field, it is used in whipped cream dispensers. In racing, it enhances engine power by allowing more fuel to burn, improving performance.

Explanation

Selenium is a semiconductor, meaning it has electrical conductivity that lies between that of metals and insulators. Its conductivity increases with exposure to light, making it useful in solar cells and photoelectric applications. Therefore, selenium is not a poor conductor of electricity.

Explanation

Option (c) is correct: Zinc oxide (ZnO) is commonly referred to as philosopher’s wool. It is known as philosopher wool due to its wool-like texture. This name comes from the historical belief that zinc oxide could be produced by heating zinc metal in air, and it was once used by alchemists in their experiments. Zinc oxide is a white powder with applications in Cosmetics (UV-blocking in sunscreens), Rubber (activator in vulcanization), Paints (pigment, mildew-resistant) and Pharmaceuticals (antiseptic in ointments). Options (a), (b) and (d) are incorrect:

Zinc bromide (ZnBr₂) is used in dry cell batteries and photography. Zinc nitrate (Zn(NO₃)₂) is used in fertilizers and as a laboratory reagent. Zinc chloride (ZnCl₂) is used in chemical production and water treatment. None of these compounds are associated with the term "philosopher’s wool," which refers to zinc oxide (ZnO).

Explanation

Option (b) is correct: German silver does not contain any silver at all. Alloy of copper (60%), nickel (20%), and zinc (20%). No actual silver content. Known for hardness, corrosion resistance, and silver-like appearance. Commonly used in jewelry, musical instruments, and coins. Options (a), (c) and (d) are incorrect:

Horn silver (also known as silver chloride, AgCl), gray, heavy halide mineral. Found in oxidized zones of silver-bearing veins. It is associated with silver and silver related minerals. Ruby silver: Collective term for pyrargyrite and proustite, both silver-bearing minerals with striking red colors. While Pyrargyrite(deep red color) is silver antimony sulfide (Ag₃ SbS₃) and Proustite (Scarlet red color) is Silver arsenic sulfide (Ag₃ AsS₃). Both crystallize in the trigonal system and possess a Mohr’s hardness of 2.5 and specific gravity of 5.82.. Lunar caustic: Another name for silver nitrate (AgNO₃). An inorganic compound containing silver. Has antiseptic properties. Used in various medical applications, including the treatment of warts and as a cauterizing agent.

Explanation

Option (b) is correct: In soldering operations, especially in electronics, the most common solder alloys are made from lead (Pb) and tin (Sn). This combination is used because it has a low melting point, which makes it ideal for joining electronic components without damaging sensitive parts. The typical composition of the solder is 60% tin and 40% lead or 63% tin and 37% lead, though lead-free soldering is becoming more common due to environmental concerns, often comprising tin with small amounts of copper, silver, or other metals. Options (a), (c) and (d) are incorrect:

Iron and tin are not commonly used together in soldering; while iron is typically used as a base metal in some electrical circuit components, it is not a part of the solder itself. Aluminium and lead are not commonly used as soldering materials either. Aluminium is difficult to solder, and its oxide layer makes it less suitable for standard soldering techniques.

Explanation

Option (c) is correct: Strontium salts (e.g., strontium carbonate or strontium nitrate) are used to produce red color in fireworks. Barium salts (e.g., barium nitrate or barium chloride) are used to produce green color in fireworks. Options (a), (b) and (d) incorrect:

Zinc and Sulphur are not typically used for color in fireworks. Zinc can be used in fireworks for producing white sparks, but not for color. Potassium and Mercury are used for purple or lilac colors, but mercury is generally not used due to its toxicity and environmental concerns. Chromium and Nickel are not commonly used for coloring in fireworks. Chromium compounds can be used for green, but they are less common compared to barium and strontium.

Explanation

Assertion (A) is false: Electron affinity generally decreases as you move down a group due to increasing atomic radii and weaker nuclear attraction for the incoming electron. Additional electron shells increase the shielding effect, further reducing effective nuclear pull. Reason (R) is true: As you go down a group, additional electron shells are added, making the atomic radius increase. This is because the outermost electrons are farther from the nucleus, and the shielding effect from inner electrons increases. Directions: The following Items consist of two statements. One labeled as the ‘Assertion (A)’ and the other as ’Reason (R)’. You have to answer these items using the code given below:(2003)

Explanation

Assertion (A) is true: Synthetic detergents, unlike soap, work efficiently in hard water because they do not form insoluble scum with calcium and magnesium ions, which are present in hard water. This enables better lathering. Reason (R) is true: Synthetic detergents are mainly non-ionic or anionic, allowing them to form soluble complexes with calcium and magnesium ions, preventing scum formation. Unlike soap, which forms insoluble salts, these detergents continue to lather in hard water. Reason (R) correctly explains Assertion (A) because synthetic detergents form soluble complexes with calcium and magnesium, preventing scum and aiding lathering in hard water. Direction: The following item consists of two statements. One labeled as the ‘Assertion (A)’ and the other as "Reason (R)". You have to answer this item using the code given below:

Explanation

Statement 1 is incorrect: Ionization potential (or Energy) increases across a period (left to right) because of increasing nuclear charge, which leads to a stronger attraction between the electrons and the nucleus, making electron removal harder. The effective nuclear charge (Z_eff) increases as protons are added, while shielding remains nearly constant.

Statement 2 is correct: Electron affinity generally becomes less negative down a group. As the atomic size increases, the added electron is farther from the nucleus and experiences greater shielding, reducing the energy released during electron addition. Across a period, electron affinity generally becomes more negative, reflecting stronger attraction to added electrons. Thus, in a group of elements, electron affinity decreases as atomic weight increases.

Statement 3 is incorrect: Electronegativity increases across a period due to increasing nuclear charge, which enhances the ability to attract bonding electrons. However, group-wise, it decreases as atomic size and shielding increase, reducing the effective pull of the nucleus on bonding electrons.