Which of the following is added in low carbon steels to prevent them from becoming porous?

Answer: Option D

Silicon increases strength and hardness but to a lesser extent than manganese. It is one of the principal deoxidizers used in the making of steels to improve soundness, silicon is detrimental to surface quality, especially in the low carbon, resulphurized grades. It aggravates cracking tendencies when the carbon content is fairly high.