Plenitude is one major cause for environmental degradation.

Correct — B, insufficiency. 'Plenitude' is a noun meaning a full and abundant supply, so its opposite is a noun naming a shortage — 'insufficiency'. A second filter settles the item even faster: plenitude, abundance, insufficiency and plethora are nouns, while 'ample' is an adjective and cannot stand in for a noun.

Why the others are wrong

• (a)
  abundance — 'Abundance' is a direct synonym of 'plenitude' — the very meaning the item asks you to reverse.
• (c)
  ample — 'Ample' means plentiful, so it agrees with 'plenitude' in sense, and as an adjective it does not even match the noun it would replace.
• (d)
  plethora — 'Plethora' means an excess or oversupply, which gives you more of 'plenitude' rather than less.

An antonym item on the noun 'plenitude' — an abundant supply — whose reverse among the choices is 'insufficiency', a shortage.

Key facts

• 'Plenitude' means fullness or an abundant supply; the related adjective is 'plentiful'.
• 'Plethora' originally meant an unhealthy excess and still carries the sense of too much.
• Scarcity, dearth, paucity and insufficiency are its standard opposites.

Common traps

• Choosing 'abundance' or 'plethora', both of which restate 'plenitude'.
• Overlooking that 'ample' is an adjective where a noun is required.

No directly related past PYQ was found.

• practice — not a real PYQ

  Select the word opposite in meaning to 'surplus'.

  • (a)excess
  • (b)glut
  • (c)deficit
  • (d)plenty
  Answer(c) deficit — a surplus is what is left over and a deficit is what is missing.
• practice — not a real PYQ

  Select the word opposite in meaning to 'plethora'.

  • (a)excess
  • (b)scarcity
  • (c)abundance
  • (d)profusion
  Answer(b) scarcity — a plethora is too much of something, and scarcity is too little.