Answer:
silver
Step-by-step explanation:
Silver is a metal at room temperature.
The physical state of matter can help us know which of these substances will be the most dense. Density deals the amount of substances per unit volume.
Solids are packed closely and have a definite and ordered arrangement of their atoms. From the list above only Silver is a solid at room temperature.
Bromine is a liquid at room temperature while chlorine and oxygen are gases at room temperature. Liquids and gases do not have more substances per unit volume compared to solids. Therefore, silver should be the most dense.