Q35. Which of the following substances has the highest resistivity?
[RRB Group D 2025-cycle Official Paper (21 August 2026, Shift 1)]
(A) Manganin
(B) Silver
(C) Tungsten
(D) Iron
Answer: (A) Manganin
Explanation: Manganin is a copper–manganese–nickel alloy with much greater electrical resistivity than the three pure metals listed. Its resistance changes very little with temperature, making it useful in precision resistance standards and meter shunts. Silver, by contrast, is an excellent electrical conductor.
Q34. Why are alloys preferred for heating elements in appliances like toasters?
[RRB Group D 2025-cycle Official Paper (3 August 2026, Shift 1)]
(A) Because they have high resistivity and do not easily oxidize at high temperatures
(B) Because they are electrical insulators
(C) Because they are electrical conductors with low resistivity
(D) They have a low melting point
Answer: (A) Because they have high resistivity and do not easily oxidize at high temperatures
Explanation: Heating-element alloys such as nichrome combine high electrical resistivity with heat resistance and resistance to oxidation. They generate substantial heat when current flows yet remain stable at operating temperatures. A good heating wire must conduct electricity, so being an insulator is not desirable.
Q33. An alloy P contains 20% copper and 80% zinc by weight. Alloy Q contains 60% copper and 40% zinc. In what ratio should P and Q be mixed to obtain an alloy containing equal amounts of copper and zinc?
[UPSC Civil Services Preliminary Examination 2026, CSAT Paper]
(A) 1 : 3
(B) 3 : 1
(C) 2 : 3
(D) 3 : 2
Answer: (A) 1 : 3
Explanation: The final mixture must contain 50% copper. Alloy P has 20% copper and alloy Q has 60%. By alligation, P : Q = (60 − 50) : (50 − 20) = 10 : 30 = 1 : 3. Zinc then also constitutes 50%.
Q32. Brass is an example of:
[RRB Group D Official Paper (17 December 2025, Shift 3)]
(A) An element
(B) A compound
(C) A homogeneous mixture
(D) A heterogeneous mixture
Answer: (C) A homogeneous mixture
Explanation: Brass contains copper and zinc mixed at the metallic level. In a uniform brass sample, the components form a homogeneous solid mixture, rather than a chemical compound with one fixed formula. Varying the proportions of copper and zinc produces brass grades with different properties.
Q31. Which of the following has a variable composition?
[RRB Group D Official Paper (11 December 2025, Shift 3)]
(A) Hydrogen chloride
(B) Water
(C) Methane
(D) Brass
Answer: (D) Brass
Explanation: Brass is a copper–zinc alloy whose proportions may change according to the intended use. Hydrogen chloride, water and methane are compounds with definite chemical formulas. Alloys generally do not have a single fixed chemical formula, because their constituent proportions can vary.
Q30. Alloy X has copper and zinc in the ratio 5 : 4, and alloy Y has them in the ratio 5 : 13. If equal quantities of X and Y are mixed, what is the ratio of copper to zinc in the resulting alloy?
[UPSC CDS-II 2025, Elementary Mathematics (14 September 2025)]
(A) 5 : 8
(B) 5 : 7
(C) 6 : 7
(D) 7 : 8
Answer: (B) 5 : 7
Explanation: Take 18 units of each alloy. X then has 10 units copper and 8 zinc; Y has 5 copper and 13 zinc. The combined alloy contains 15 copper and 21 zinc, giving the reduced ratio 5 : 7.
Q29. Which copper-based alloy is preferred for making standard resistors because of its high resistivity and low temperature coefficient?
[RRB NTPC Undergraduate CBT-I (4 September 2025, Shift 3)]
(A) Alnico
(B) Manganin
(C) Tungsten
(D) Brass
Answer: (B) Manganin
Explanation: Manganin consists mainly of copper with manganese and nickel. Its comparatively high resistivity is useful in resistor construction, while its very small temperature coefficient helps resistance remain stable during measurement. These properties make manganin suitable for standard resistors and instrument shunts.
Q28. Why is an alloy considered a mixture even though it cannot be separated by ordinary physical methods?
[RRB NTPC Undergraduate CBT-I (13 August 2025, Shift 3)]
(A) It is formed only by non-metals
(B) It shows the properties of its constituents and can have variable composition
(C) It contains only one type of element in vapour form
(D) All alloys are magnetic because their composition is fixed
Answer: (B) It shows the properties of its constituents and can have variable composition
Explanation: An alloy combines elements without necessarily producing a single compound of fixed stoichiometry. Its component proportions can vary, and its physical characteristics depend on those constituents. Separating atoms within a solid alloy is difficult, but difficulty of separation does not make it a pure compound.
Q27. Assertion (A): An alloy of lead and tin is generally used for fuse wire.
Reason (R): Lead–tin alloy has a higher melting point than copper and aluminium.
Choose the correct statement.
[UPPSC PCS Preliminary Examination 2025, General Studies Paper I]
(A) Both A and R are true, and R correctly explains A
(B) A is true, but R is false
(C) A is false, but R is true
(D) Both A and R are true, but R does not explain A
Answer: (B) A is true, but R is false
Explanation: Traditional fuse alloys may use lead and tin because they melt at temperatures much lower than copper or aluminium. Excess current raises the wire temperature until it breaks the circuit. Therefore the assertion is correct but the claimed higher melting point is false.
Q26. Bronze is an alloy of:
[MPSC Group B Combined Preliminary Examination 2024 (held 2 February 2025)]
(A) Copper and tin
(B) Copper and zinc
(C) Copper and lead
(D) Copper and nickel
Answer: (A) Copper and tin
Explanation: Bronze traditionally combines copper with tin. Adding tin increases copper’s hardness and improves several wear and corrosion properties. Bronze has long been used for sculptures, coins, tools, bearings and other cast articles. Brass, in comparison, is primarily copper and zinc.
Q25. Which type of alloy is formed when a metalloid or non-metal is dissolved in a metal?
[DSSSB Assistant Engineer (Civil) Official Paper (22 June 2024, Shift 2)]
(A) Composite alloy
(B) Interstitial alloy
(C) Amorphous alloy
(D) Substitutional alloy
Answer: (B) Interstitial alloy
Explanation: In an interstitial alloy, comparatively small atoms occupy spaces between the larger metal atoms in the crystal lattice. Carbon in iron is a familiar example. Such solute atoms impede dislocation movement and can increase hardness and strength, depending on composition and treatment.