What? That docent make any scene?
It's the rows. They are periods. (1,2,3,4,5,6,7 - the ones without the letters).
Calcium forms an ionic bond to iodine and forms calcium iodide (CaI2). The calcium atom gives away 2 of its valence electrons, one to each of the 2 iodine atoms thus forming the ionic bond.
Answer:
B. Ca
Explanation:
Let's look at the electron configurations of all four elements (I am going to write it in noble gas configuration to make it simpler):
Mg electron configuration: [Ne]3s2
Ca electron configuration: [Ar]4s2
Ar electron configuration: [Ar]
K electron configuration: [Ar] 4s1
We notice that Ca has two electrons in the 4s sublevel, which satisfies what the question is asking for.
The answer is thus B. Ca.