Final answer:
The element with the electron configuration [Ar]4s2 3d10 4p5 is bromine (Br), a halogen that forms an anion with a 1- charge by gaining one electron.
Step-by-step explanation:
The electron configuration of [Ar]4s23d104p5 indicates that the element is one electron short of having a full p subshell. This configuration corresponds to the element bromine (Br), which is in the halogen group. Halogens are known for having seven electrons in their outermost p subshell and for their tendency to gain one electron to achieve a noble gas electron configuration, forming an anion with a 1- charge.
Therefore, the statements that are true about the element with this electron configuration are: The element is a halogen, The element has one fewer electron than the following noble gas, and When the element reacts with a metal, the element tends to gain one electron to form an anion with a 1- charge. The statement that The element is Se is incorrect because selenium (Se) has an electron configuration of [Ar]4s23d104p4.