67th BPSC Prelims Re-exam 2022
General Science Previous Year Questions (PYQs)

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.