67th BPSC Prelims Re-exam 2022 Question Paper

Detailed Explanation:

Carbohydrates are broken down during digestion into their simplest absorbable form, glucose, which is a monosaccharide. All complex carbohydrates (polysaccharides like starch) and disaccharides (like maltose, sucrose) are ultimately degraded to glucose for cellular absorption and energy production.

Glycerol is derived from lipid metabolism, maltose is a disaccharide that further splits into two glucose molecules, and amino acids are the end products of protein digestion.

Therefore, glucose is the ultimate degradation product of carbohydrates, making Option 2 the correct answer.

Detailed Explanation:

Earthworms lack red blood cells (RBCs); their respiratory pigment hemoglobin is dissolved directly in the plasma, not packed inside cells.

Snakes and peacocks are vertebrates that possess RBCs containing hemoglobin for oxygen transport.

Therefore, only earthworm is without red blood cells, making Option 1 the correct answer.

Detailed Explanation:

Chloroquine is an antimalarial drug used for treatment and prophylaxis of malaria, making this pair correctly matched.

Tuberculosis is prevented by BCG vaccine (not ATS); Tetanus is prevented by tetanus toxoid (not BCG); Scurvy results from vitamin C deficiency (not thiamine/vitamin B1).

Therefore, only Malaria-Chloroquine is correctly matched, making Option 3 the correct answer.

Detailed Explanation:

Pine, Fir, Spruce, Cedar, Larch, and Cypress are all conifers, which belong to gymnosperms—seed plants with naked seeds borne on cones, not enclosed in ovaries.

Angiosperms are flowering plants with seeds in fruits; monocotyledons and dicotyledons are angiosperm subdivisions. These timber trees lack flowers and produce exposed seeds on cone scales.

Therefore, all listed timber-yielding plants belong to gymnosperms, making Option 1 the correct answer.

Detailed Explanation:

Soil is the primary source of essential mineral nutrients for plants, including nitrogen, phosphorus, potassium, calcium, magnesium, and micronutrients like zinc and iron. These nutrients are absorbed by roots in ionic forms dissolved in soil water.

The atmosphere provides carbon dioxide for photosynthesis, and light drives photosynthesis, but neither supplies mineral nutrients. Chlorophyll is a pigment that captures light energy, not a nutrient source.

Therefore, soil is the main nutrient reservoir for plants, making Option 3 the correct answer.

Detailed Explanation:

Pollination is precisely defined as the transfer of pollen grains from the anther (male part) to the stigma (female part) of a flower. This is the actual act of pollination, distinct from subsequent reproductive processes.

Germination of pollen grains and growth of the pollen tube occur after pollination is complete. Insect visitation is merely a mechanism (agent) of pollination, not the process itself.

Therefore, the transfer of pollen grain from anther to stigma is the correct definition, making Option 4 the correct answer.

Detailed Explanation:

Fungi are heterotrophic organisms that lack chlorophyll, the pigment essential for photosynthesis. Without chlorophyll, they cannot synthesize their own food from sunlight and must absorb nutrients from organic matter in their environment.

They require oxygen (most are aerobic), utilize carbon dioxide in respiration, and grow in various light conditions—thus these components are not lacking. Their cell walls contain chitin, distinguishing them from true plants.

Therefore, chlorophyll is the key component fungi lack, making Option 2 the correct answer.

Detailed Explanation:

Halophytes are plants specially adapted to survive in high-salt environments, tolerating concentrations up to 1M NaCl. Common examples include mangroves and salt marsh vegetation.

Xerophytes thrive in dry/desert conditions, Mesophytes in moderate environments, and Glycophytes are salt-sensitive plants that cannot tolerate saline conditions.

Therefore, salt-loving plants are Halophytes, making Option 3 the correct answer.

Detailed Explanation:

Strontium compounds (like strontium carbonate) emit a bright red colour when heated in fireworks. The heat excites electrons in strontium atoms, which release energy as red light when returning to ground state.

Sodium produces yellow, sulphur burns but doesn't produce metal flame colours, and magnesium gives white light.

Therefore, strontium is responsible for bright red colour in crackers, making Option 4 the correct answer.

Detailed Explanation:

Biogas is produced by anaerobic digestion of organic matter and contains 50–70% methane (CH₄), which is its primary combustible component.

Propane, butane, and ethane are constituents of petroleum gas and natural gas, not biogas.

Therefore, methane is the main constituent of biogas, making Option 4 the correct answer.

Detailed Explanation:

Salt (NaCl) is a non-volatile solute that causes boiling point elevation and freezing point depression through colligative properties—saltwater boils at a higher temperature and freezes at a lower temperature than pure water.

Methyl alcohol (methanol) is a volatile solute with higher vapor pressure than water. When added to water, it increases the overall vapor pressure of the mixture, causing the boiling point to decrease.

Therefore, both statements correctly describe opposite effects due to different solute types, making Option 3 the correct answer.

Detailed Explanation:

Noble metals (gold, silver, platinum, and platinum-group metals) are chemically inert, resist corrosion, and are typically found in pure native form in nature due to their nonreactive properties.

• Statement 1 is Correct: Noble metals like gold and platinum occur naturally in uncombined, pure metallic state.
• Statement 2 is Incorrect: Uranium and lead are highly reactive metals that occur as ores (e.g., uraninite, galena), not as noble metals.
• Therefore, only Statement 1 is correct, making Option 4 the correct answer.

Detailed Explanation:

Platinum is a lustrous, dense, silver-white precious metal with high corrosion resistance and catalytic properties. It is commonly referred to as white metal due to its natural silvery-white appearance.

Gold is yellow, copper is reddish-brown, and cobalt is greyish-blue—none match the white metal descriptor. While industrial alloys of tin/lead are sometimes called "white metal," in UPSC/general knowledge context, platinum is the standard answer.

Therefore, platinum's silvery-white color makes Option 2 the correct answer.

Detailed Explanation:

Rusting is oxidation of iron (4Fe + 3O₂ → 2Fe₂O₃·xH₂O), where oxygen and water molecules bond to iron atoms, increasing total mass as hydrated iron oxide forms.

Over time, the rust layer flakes off or detaches from the surface due to its brittle nature, causing the overall weight to decrease.

Therefore, the weight first increases (oxidation) then decreases (flaking), making Option 2 the correct answer.

Detailed Explanation:

Quicklime is the common name for calcium oxide (CaO), produced by heating limestone (CaCO₃) to drive off carbon dioxide.

Ca(OH)₂ is slaked lime (formed when quicklime reacts with water), CaCl₂ is calcium chloride, and CaCO₂ is not a valid chemical formula.

Therefore, CaO is quicklime, making Option 4 the correct answer.

Detailed Explanation:

Brass is an alloy composed primarily of copper (Cu) and zinc (Zn). The proportion of these two metals can vary (typically 55–95% copper, 5–45% zinc), affecting properties like color, hardness, and corrosion resistance.

Other options are incorrect: Iron and zinc do not form brass; copper and nickel form cupronickel; iron and copper is not a standard brass alloy.

Therefore, zinc and copper are the constituents of brass, making Option 4 the correct answer.

Detailed Explanation:

Smelting is the metallurgical process where ore is heated with a reducing agent (like coke) to extract the metal in a fused (molten) state, separated from slag.

Roasting converts sulfides to oxides in excess air, calcination removes volatile impurities in limited air, and froth flotation is a physical concentration method—none produce molten metal directly.

Therefore, only smelting yields metal in a fused state, making Option 4 the correct answer.

Detailed Explanation:

The nucleus of an atom contains protons (positively charged) and neutrons (neutral), forming the dense central core discovered by Rutherford in 1911.

Electrons orbit outside the nucleus in electron clouds—they are not part of the nuclear structure.

Therefore, only protons and neutrons constitute the nucleus, making Option 2 the correct answer.

Detailed Explanation:

Paramagnetic substances are weakly attracted by magnetic fields and have small positive susceptibility (χ > 0). Among the options, platinum is a classic paramagnetic material with unpaired electrons that align weakly with external magnetic fields.

Iron and nickel are ferromagnetic (strongly magnetic, χ >> 1000), while mercury is diamagnetic (weakly repelled, χ < 0). Other paramagnetic examples include aluminium and manganese.

Therefore, only platinum exhibits paramagnetic behavior, making Option 3 the correct answer.

Detailed Explanation:

A convex lens is thicker at the center and converges light rays. When an object is placed between the lens and its focal point, it produces a magnified, upright, virtual image—the principle behind magnifying glasses.

Concave lenses and plano-concave lenses diverge light and reduce image size, while convex mirrors also produce diminished images, making them unsuitable for magnification.

Therefore, a convex lens is used in magnifying glasses, making Option 2 the correct answer.