CDS (I) 2021 General Knowledge · Question 102 of 120

Correct — B, Au. Gold is the most malleable metal known — a single gram can be beaten into a sheet about a square metre in area, and gold leaf can be made thin enough to be semi-transparent. It is the most ductile as well: gold can be drawn into a wire one atom wide and then stretched further before it snaps. Malleability is the ability to be hammered into sheets and ductility the ability to be drawn into wire, and gold holds the record for both, which is why gold leaf covers domes and manuscripts and why fine gold wire is used for the connections inside microchips. Both properties are properties of a solid metal, and that fact alone removes one of the wrong options here.

• (a)Na — Sodium is soft enough to cut with a knife, which is not the same as malleable — it crumbles rather than spreading into a sheet, and it is far too reactive to be drawn or worked in air.
• (c)Ce — Cerium is a lanthanide and workable, but it tarnishes rapidly in air and is never the reference example. Nothing about it makes it a better answer than the metal that holds both records.
• (d)Hg — Mercury is liquid at room temperature. A liquid cannot be hammered into a sheet or drawn into a wire, so it is disqualified from both properties at once.

Metals deform without breaking because their atoms sit in layers held by a shared sea of electrons; a blow slides one layer over another while the metallic bonding survives the move. Hammering out that sliding gives sheets, which is malleability; pulling it out gives wire, which is ductility. Gold and silver are the standard examples of both, and the same bonding also explains why metals are lustrous, sonorous and good conductors.

The list is written in symbols rather than names, so the first task is reading it: Na is sodium, Au gold, Ce cerium, Hg mercury. Mercury goes first, on the ground that a liquid can be neither hammered nor drawn. Sodium goes next, because softness and malleability are different things. That leaves gold and cerium, and gold is the element every textbook cites for both properties at once — the question says 'both', and gold is the only one on the list that carries both records. Working the item through symbols is the intended difficulty; a candidate who reads Au as silver or Ce as copper will land somewhere else entirely.

• Gold is the most malleable metal — one gram can be beaten into a sheet of about one square metre.
• Gold can be drawn into a wire of single-atom width and stretched considerably before breaking.
• Malleability is the ability to be hammered into thin sheets; ductility is the ability to be drawn into wire.
• Gold's symbol Au comes from the Latin aurum, and gold is one of the least reactive of all the elements.
• Mercury, symbol Hg, is the only metal that is liquid at ordinary room temperature.

• Reading the symbols wrongly — Au is gold, Ag is silver, and Ce is cerium rather than copper.
• Equating sodium's softness with malleability.
• Forgetting that mercury is a liquid, and so cannot show either property.

As a property-to-element item, often written in symbols so that reading the periodic table is part of the test.

• practice — not a real PYQ

  The property of a metal that allows it to be drawn into thin wires is called

  • (a)malleability
  • (b)ductility
  • (c)sonority
  • (d)lustre

  Answer(b) ductility — drawing into wire is ductility, while hammering into sheets is malleability; gold is the leading example of both.

• practice — not a real PYQ

  Which one of the following metals is a liquid at ordinary room temperature?

  • (a)Sodium
  • (b)Gallium
  • (c)Mercury
  • (d)Cerium

  Answer(c) Mercury — the only metal that is liquid at ordinary room temperature; gallium melts a little above it, at about 30 °C, and will melt in the hand.