Choose the correct one-word substitution for the sentence below.
"In his extreme old age when he behaves like a fool, people often lose patience with him."

Correct option is D

The correct one-word for the given group of words is (right option) Dotage.
In extreme old age, people may show childish or foolish behavior; this condition is called dotage, which specifically denotes the senile decline marked by folly or weak judgment in old age. (Hindi: वार्धक्य में मूढ़ता/बुढ़ापे की सठियाहट)
Example: In his dotage, he trusted every scam caller who promised him riches.
Meanings of the given other options:
· Imbecility: weakness of mind; extreme stupidity (Hindi: मंदबुद्धि/मूर्खता) — not restricted to old age.
· Superannuation: retirement due to age; pensioning off (Hindi: सेवानिवृत्ति) — administrative status, not behavior.
· Senescence: the process/state of growing old (Hindi: बुढ़ापा/वृद्धावस्था) — neutral aging, not necessarily foolish behavior.