The answer to your query is as follows:
· The thought was almost revolting: The thought of the author’s old grandmother being young and pretty, in early years of her life, raised a conflict in the mind of the author.
· An expanse of pure white serenity:
This simile is used to describe the calmness and peaceful character of the author’s grandmother, as compared to the winter landscape in the mountains. It draws a picture of contentment.
· A veritable bedlam of chirruping:
A genuine creations of noise or confusions is caused by the chirruping of the sparrows which scattered and perched around the author’s grandmother.
· Frivolous rebukes:
The author’s grandmother criticized or checked on the sparrows, in vain. Her sharp reprimands were of little importance to the sparrows, as the latter couldn’t understand human language.
· The sagging skins of the dilapidated drum:
The deteriorated condition of the drum has been described here. The author’s grandmother played this broken drum even though it was falling into a state of disrepair.
Hope you are satisfied!