Q4. Evaluate these material–chemical pairs:
(1) lipstick–lead,
(2) soft drinks–brominated vegetable oils,
(3) Chinese fast food–monosodium glutamate.
Which match?
[UPSC Civil Services Preliminary GS-I, 2017]
(A) 1 only
(B) 2 and 3 only
(C) 1 and 3 only
(D) 1, 2 and 3
Answer: (D) 1, 2 and 3
Explanation: Lead contamination in some lipsticks, brominated vegetable oils historically used in certain soft drinks, and monosodium glutamate used as a flavour enhancer in some Chinese-style fast foods have all raised chemical-use discussions. The examination regarded all three pairs as correctly matched.
Q3. Which examples demonstrate corrosion: blackening of silver, greening of copper, or browning of iron?
[CGPSC Preliminary General Studies 2016 Official Paper]
(A) Black coating on silver
(B) Green coating on copper
(C) Brown coating on iron
(D) All three
(E) None of these
Answer: (D) All three
Explanation: Silver can develop black silver sulfide tarnish; copper commonly develops a green patina; and iron forms reddish-brown rust under suitable conditions. Each is an example of a metal undergoing chemical deterioration through reactions with its surroundings.
Q2. Which substance reacts with glass and therefore should not normally be stored in glass containers?
[WBCS Preliminary 2015 Official Paper]
(A) HNO₃
(B) HCl
(C) HF
(D) HBr
Answer: (C) HF
Explanation: Hydrofluoric acid attacks silica, a major constituent of glass, by forming silicon-fluoride species. Consequently, HF is commonly handled in compatible plastic containers rather than glass vessels. The other listed mineral acids do not characteristically etch ordinary glass in this way.
Q1. What is the molecular geometry of sulphur hexafluoride (SF₆)?
[45th BPSC Preliminary Examination, 2002]
(A) Trigonal pyramidal
(B) Octahedral
(C) Planar
(D) Tetrahedral
Answer: (B) Octahedral
Explanation: Sulphur hexafluoride has six fluorine atoms bonded to a central sulphur atom. The six bonding directions arrange symmetrically toward the corners of an octahedron, with approximate F–S–F bond angles of 90 degrees. Therefore, SF₆ has octahedral molecular geometry.
