Question

In which pair is the one on the left larger than the one on the right?

1. S, Mg
2. K, K+
3. Na, Rb
4. Br, Br-

Answer 1

K because parent atoms are always larger than their cations(positively charged atoms)

Answer 2

K is larger than K+

Step-by-step explanation:

Given that the atomic radius is affected by the number of electrons arround the nucleus (being the numeber of protons constant). The lower the number of electrons, the stonger is the atraction between them and the protons resulting on a smaller atomic radius.

The K+ is a monovalent cation of K, meaning that it has 1 less electron than K and therefore a smaller radius.