One of the statements below contains a word used incorrectly or inappropriately. Choose the option which has the incorrect or inappropriate usage of the word.

The question is testing for word usage between callus and callous.

A callus is that tough, hardened patch of skin you get on your hands from gripping monkey bars too much or on your feet from wearing shoes that don't fit quite right. Think of it as your body's natural armor - it builds up to protect you from repeated friction or pressure, like a protective shield made of dead skin cells.

Callous, on the other hand, describes someone who's emotionally hardened - like they've built up thick emotional skin that makes them insensitive to others' feelings. If your friend doesn't even blink when you tell them about your pet goldfish dying, you might say they're being callous about your loss.

Option 1 -> Correctly uses "callus" to refer to hardened skin causing discomfort.

Option 2 -> Correctly uses "callus" to refer to hardened skin being examined by a doctor.

Option 3 -> Correctly uses "callus" to refer to hardened skin protecting the foot.

Option 4 -> Incorrectly uses "callus" when it should be "callous" - the phrase should be "callous indifference" meaning cruel, unfeeling indifference.

Hence, Option 4 is correct