Based on the periodic table and general trends in malleability, phosphorus (P) is likely the least malleable element in its solid state.
Malleability tends to increase as you move from nonmetals to metals. Antimony (Sb) is a metalloid, strontium (Sr) is an alkaline earth metal, and copper (Cu) is a metal known for its high malleability. In contrast, phosphorus is a nonmetal and is brittle in its solid form, making it the least malleable of the options provided.
So, the correct response is:
phosphorus (P).