Sort of acid acceptable around most of vast country (7)

'sort of acid' is the definition.
(prussic acid is hydrogen cyanide)

'acceptable around most of vast country' is the wordplay.
'acceptable' becomes 'pc' (abbreviation for politically correct).
'around' indicates putting letters inside.
'most of' means to remove the last letter.
'vast country' becomes 'russia'.
'russia' with its last letter taken away is 'russi'.
'pc' placed around 'russi' is 'PRUSSIC'.