Final answer:
The original form of fluoride is the ion F-, while krypton is denoted as Kr, representing the element itself uncharged. The correct answer is option (a): Fluoride: F-; Kr: Krypton. Krypton does not typically form ions, hence why it is just represented as Kr.
Step-by-step explanation:
The original form of fluoride is F-, which indicates that it is a negatively charged ion of fluorine. Fluorine as an element is denoted as F, so when it is in its ionic form with an extra electron, it becomes fluoride with the chemical formula F-. On the other hand, Kr stands for the element krypton, which is a noble gas and does not typically form ions under normal conditions. Therefore, its original form is simply Kr, uncharged and as an individual atom.
So, to answer the student's question, the original forms are: a) Fluoride: F-; Kr: Krypton. This corresponds to option (a) from the question provided.
Referring to the oxidation numbers, we can assign them to different substances. For example, in lithium hydride (LiH), lithium has an oxidation number of +1 and hydrogen has -1. In potassium peroxide (K2O2), potassium has an oxidation number of +1 and peroxide has -1 per oxygen (as peroxide is an O22- ion). Lastly, in potassium fluoride (KF), potassium has an oxidation number of +1 and fluoride has -1.