Final answer:
The correct order of the elements A, B, and C beneath Rubidium (Rb) is Rb, C, A, B.
Step-by-step explanation:
The correct order of the elements A, B, and C beneath Rubidium (Rb) is option b) Rb, C, A, B. The first ionization energy refers to the energy required to remove an electron from an atom, and it generally increases from left to right across a period and decreases down a group in the periodic table. Electronegativity is a measure of an atom's tendency to attract electrons in a chemical bond, and it follows a similar trend. The atomic radius, on the other hand, generally increases from right to left across a period and from top to bottom within a group.