The correct option is C tensile strength to the alloy
In addition to iron, carbon, and chromium, modern stainless steel may also contain other elements, such as nickel, niobium, molybdenum, and titanium. Nickel, molybdenum, niobium, and chromium enhance the corrosion resistance of stainless steel.
So stainless steel contains in addition to iron - nickel and chromium which imparts tensile strength to the alloy.