Find the word that is spelled correctly and means the quality of being sarcastic in a bitter way.

Correct — A. Caustic means burning or corrosive, as in caustic soda. Of remarks, it means bitterly sarcastic.

The quality takes -ity, and the c of caustic stays: caustic + ity = causticity, just as electric gives electricity.

Causticity → option (a).

Why the others are wrong

• (b)
  Costicity — Costicity writes the first vowel as it sounds. Caustic is spelt with au, and the au carries into causticity.
• (c)
  Cawstic — Cawstic writes aw for au, and it is the bare adjective, not the quality. It lacks the -ity the question asks for.
• (d)
  Caustisity — Caustisity turns the c before -ity into s. The suffix joins caustic unchanged, so the ending must be -city.

This item joins a meaning to a spelling. Sarcastic in a bitter way is the figurative sense of caustic, and 'the quality of' asks for the noun.

First check: the stem is caus-, with au, not o or aw.

Second check: the suffix -ity attaches to a word ending in -ic without changing the c, which is then said like s: elastic, elasticity.

Key facts

• Caustic = corrosive (chemistry), and bitingly sarcastic (of remarks).
• Causticity = the quality of being caustic.
• -ic + -ity keeps the c: electric → electricity, elastic → elasticity.

Common traps

• Spelling by sound: cost- or caws- instead of caus-.
• Writing -sity because the ending is said with an s sound.

No directly related past PYQ was found.