You no doubt mean krematorium II and Krematorium III, which housed the largest gas chambers. They were not the only extemination complexes on Auschwitz, but they were where most people were killed.
Auschwitz I- Birkenau
There was one large extermination camp in Auschwitz II (Birkenau).
Auschwitz I was the original Auschwitz camp, set up in May 1940, mainly for Polish political prisoners and the Polish elites. It also housed the main administrative offices for the whole complex of camps as well as the blocks where medical experiments were carried out, and execution chambers.
Auschwitz was a concentration camp.concentration and extermination camp
mainly extermination
Auschwitz.
A Extermination camp
A large combined concentration and extermination death camp for Jews
From early 1942 Auschwitz operated as both. The only other camp that served as both a concentration camp and extermination camp was Majdanek.
Concentration camp and Extermination camp
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It was an extermination camp for Jews.