First Lady: “I’m obliged to ingest nerve gas” (7)
I believe the answer is:
tsarina
'first lady' is the definition.
'tsarina' can be an answer for 'lady' (I have seen 'lady of importance' mean 'tsarina' so perhaps 'lady' could also mean 'tsarina'). I'm not sure about the 'first' bit.
'i'm obliged to ingest nerve gas' is the wordplay.
'i'm obliged' becomes 'ta' (I am not sure about this - if you are sure you should believe this answer much more).
'to ingest' is an insertion indicator (inserted letters are ingested or eaten).
'nerve gas' becomes 'sarin' (I've seen this before).
'ta' going around 'sarin' is 'TSARINA'.
Can you help me to learn more?
(Other definitions for tsarina that I've seen before include "Russian empress (S, not Z)" , "lady of some importance" , "Consort" , "top Russian women" , "Monarch" .)