Alloys

Total Questions: 42

31. In the case of rusting, the weight of iron— [U.P.P.C.S. (Mains) 2008, M.P.P.C.S. (Pre) 1991]

(a) Increases
(b) Decreases
(c) Remains the same
(d) Uncertain

Correct Answer: (a) Increases

Solution:Rusting is a chemical process (oxidation) where iron reacts with oxygen and moisture (water) to form hydrated iron(III) oxide (Fe₂O₃·nH₂O), which is commonly known as rust. During this process, oxygen atoms from the atmosphere are added to the iron atoms. According to the law of conservation of mass, the total mass of the reactants must equal the total mass of the products. Since the iron combines with oxygen (and water), the resulting rust will weigh more than the original iron alone.

32. What happens to the weight of iron when it rusts? [67th B.P.S.C. (Pre) (Re. Exam) 2022]

(a) Increases for a long time
(b) Decreases, then increases
(c) Increases, then decreases
(d) Remains the same
(e) None of the above/More than one of the above

Correct Answer: (a) Increases for a long time

Solution:Due to rust, the weight of iron increases as iron is converted into iron oxide after a chemical reaction with oxygen in the presence of humidity.

33. Consider these statements and choose the right answer from the given code: [U.P. Lower Sub. (Pre) 1998]

Statement (A): Normally it has been seen that iron goods covered with a brown powder called rust when they are unsheltered in the atmosphere.

Statement (R): Rust or the brown powder is the result of the deposition of tannin.

Code:

(a) Both (A) and (R) are correct, and (R) is the right explanation of (A).
(b) Both (A) and (R) are correct, but (R) is not the right explanation of (A).
(c) (A) is correct, but (R) is wrong.
(d) (A) is wrong, but (R) is correct.

Correct Answer: (c) (A) is correct, but (R) is wrong.

Solution:Statement (A) is correct, but statement (R) is wrong because rust is iron oxide (not tannin), a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Tannin is a pale-yellow to light-brown substance secreted from plants and used chiefly in tanning leather, dyeing fabric, making ink, and in various medical applications.

34. Which of the following elements is added to iron to produce steel which can resist high temperature, have high hardness and abrasion resistance? [I.A.S. (Pre) 1996]

(a) Aluminium
(b) Chromium
(c) Nickel
(d) Tungsten

Correct Answer: (b) Chromium

Solution:Stainless steel is a steel alloy with a minimum of 10.5% Chromium content by mass. The presence of Chromium protects steel from corrosion, rust, and makes it high-temperature resistant.

35. The important metal used with iron to make it rust-free— [Chhattisgarh P.C.S. (Pre) 2011]

(a) Aluminium
(b) Carbon
(c) Chromium
(d) Tin

Correct Answer: (c) Chromium

Solution:Stainless steel is a steel alloy with a minimum of 10.5% Chromium content by mass. The presence of Chromium protects steel from corrosion, rust, and makes it high-temperature resistant.