ANS:A - are free from oxygen.

Killed steels are steels that have been treated with a strong deoxidizing agent such as aluminum or silicon to remove excess oxygen from the molten metal before casting. Therefore, the correct statement regarding killed steels is:

• Killed steels are free from oxygen.

This deoxidation process helps to prevent the formation of gas bubbles and porosity in the solidified steel, resulting in a more uniform and defect-free final product. Killed steels are commonly used in applications where a smooth and consistent surface finish is required, such as automotive body panels, pipelines, and structural components. The other statements provided are not necessarily true for all killed steels:

• While killed steels are generally low in oxygen content, they may still contain trace amounts of sulfur and phosphorus, although these impurities are typically minimized.
• Killed steels can be produced by various steelmaking processes, not only by the LD (Linz-Donawitz) process. The LD process, also known as the basic oxygen process, is one of the methods used for producing steel, but there are other methods such as electric arc furnaces (EAF) and open hearth furnaces.
• While killed steels are typically controlled for impurity levels, the term "minimum impurity level" is not universally applicable. The impurity levels can vary depending on the specific steel grade and its intended application.