Which two electron configurations represent elements that would have similar chemical properties? (1) 1s22s22p4 (2) 1s22s22p5 (3) [ar]4s23d5 (4) [ar]4s23d104p5?

Two electron configurations of elements that would have similar chemical properties are (2) and (4).

Explanation:

(1)

(2)

(3)

(4)

Valence electrons : These are the electrons present in last principal quantum number of an atom of the element.

Two electron configurations represent elements that would have similar chemical properties are (2) and (4). This is because number of valence electrons present in both of them are same that is seven valence electrons . Also valence electrons of both the elements are present in p-orbital which means that they both belongs to same group  in a periodic table. The members of same group in a periodic table have similar chemical properties.

if you mean hydrogen and oxygen then water is the product