ANS:A - 0.2

The minimum carbon content in steel should be approximately 0.2 percent for it to respond effectively to a hardening treatment. Carbon content significantly influences the hardenability of steel, which refers to its ability to be hardened by heat treatment processes such as quenching and tempering. Steels with higher carbon content can achieve greater hardness and strength after heat treatment compared to low-carbon steels. While the exact minimum carbon content for hardenability can vary depending on the specific steel grade and desired properties, a carbon content of around 0.2 percent is generally considered sufficient for most steel grades to respond effectively to hardening treatments. Therefore, the closest option is: 0.2 percent