The correct answer is (a) Austenitic
The explanation is: Steel is classified into austenitic, ferritic, martensitic and duplex depending upon the percentages and different materials used for forming them. Austenitic steel consists of 0.15% carbon and 16% of chromium, nickle and/or manganese. Sometimes titanium may be added to improve strength. Austenitic steel forms a series from number 300. 316 and 316L are used to make biomedical implants like a stent.