The elements Lithium (Li), Boron (B), and Oxygen (O) are all in the same on the periodic table.

Period

Explanation:

If we ubicate te period one on the alkaline metals, we can see the lithium, so we go to the borans on te group AIII an we see Boron, move to the rigth on the same sense tou the group AVI we see the Oxygen, we can know that also for the electronic configuration Li:1s²2s¹    B:1s²2s²3p

14 days is the half-life of phosphorus-32

the answer is option a.