Difference between "acrid" and "acidulous"

English as a Second Language Preparation forum for the GRE® Test
1

This is a question in TEST # GRE/W97:

  1. adj. harsh or corrosive in tone; bitter; blistering; caustic; virulent

(a) sensual
(b) porous
© acidulous
(d) acrid

The given answer is (d) " acrid", of course it’s undoubtedly correct. I wonder whether the option © “acidulous” can possibly be another acceptable answer.

2

“An acidulous tone had crept into both sides of the conversation, her side with balsamic asseverations and cloying evasions, his with a bite of horseradish astride a malt vinegar redolent of London fogs, fish and chips, and tabloid treacle and gossip (it was, in fact, revolting).”

It seems acidulous is not that harsh.