Bacillus used to test the efficacy of Sterilization by Autoclave is?
Bacillus subtilis.
Bacillus pumilus
Bacillus stearothermophilus
Coxiella burnetii
Various bacilli are used to check the efficacy of sterilization methods are:

Autoclave- Bacillus stearothermophilus
Hot air oven- Bacillus subtilis subspecies niger
Ionising radiation- Bacillus pumilus