Question

When chromium loses two electrons, its configuration changes to

A. [Ar]4s13d5.
B. [Ar]4s1.
C. [Ar]4s13d4.
D. [Ar]3d4.

Answer 1

Electronic configuration of cromium is  

Cr-[Ar]4s¹3d⁵  

When cromium loses two electrons it becomes Cr⁺².  

So its electronic configuration becomes,  

Cr⁺²-[Ar]3d⁴  

One electron will go from 4s orbital and one electron will go from 3d orbital.

So the answer here is D. [Ar]3d⁴ -because after losing 2 electrons electronic configuration of cromium becomes  [Ar] 3d⁴.