Final answer:
The oxidation numbers for potassium and chloride in KCl are +1 and -1 respectively, which corresponds to option B. Potassium, as an alkali metal, typically has an oxidation number of +1, while chlorine as a halide has an oxidation number of -1.
Step-by-step explanation:
To determine the oxidation numbers for potassium and chloride in KCl, we refer to rule six, which states that in a neutral molecule, the sum of the oxidation numbers must be 0. Potassium is part of the alkali metal group and when it forms ions, it typically has a charge of 1+, giving it an oxidation number of +1. This is in accordance with guideline 2 mentioned above for monatomic ions.
As for chlorine, it is halogen, and when it forms halide compounds, it typically has a negative oxidation number. In KCl, it exists as a chloride ion with an oxidation number of -1. So, the correct answer is B. 1+ for K and 1- for Cl.
To summarise, in KCl, which is an ionic compound, we conveniently assign oxidation numbers for the cation (potassium) and anion (chloride) separately, resulting in +1 for potassium and -1 for chloride.