ANS:A - machinability

Tempering of a material does not improve its machinability. Tempering is a heat treatment process that follows hardening (quenching) and is typically used to reduce the hardness and brittleness of a previously hardened material while improving its toughness and ductility. During tempering, the material is heated to a specific temperature below its critical point and then allowed to cool in still air. While tempering improves the toughness, ductility, and impact resistance of a material by relieving internal stresses and refining the microstructure, it does not directly affect its machinability. Machinability refers to how easily a material can be machined (cut, drilled, or shaped) using various cutting tools and machining processes. Factors influencing machinability include the material's hardness, strength, thermal conductivity, and chemical composition. Therefore, of the options provided, tempering does not improve the machinability of a material.