Answer is: a. Rubidium (Rb) is more reactive than strontium (Sr) because strontium atoms must lose more electrons.
The ionization energy (Ei) is the minimum amount of energy required to remove the valence electron, when element lose electrons, oxidation number of element grows (oxidation process).
Alkaline metals (group 1), in this example rubidium, have lowest ionizations energy and easy remove valence electrons (one electron), they are most reactive metals.
Earth alkaline metals (group 2), in this example strontium, have higher ionization energy than alkaline metals, because they have two valence electrons, they are less reactive.
Rubidium electron configuration: ₃₇Rb 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶5s¹; one valence electron is 5s¹ orbital.
Strontium electron configuration: ₃₈Sr 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶5s²; two valence electrons is 5s² orbital.
<h3><u>Kupier Belt:</u></h3>
<u>Location:</u>
Kuiper belt also known as Edgeworth-Kuiper belt which is in the shape of "flat ring of icy small bodies" that revolve around the Sun beyond the orbit of the planet Neptune. It is a "circumstellar disc" that is similar to the "asteroid belt" in the outer solar system.
<u>Composition: </u>
Its composition mainly consists of "small bodies or remnants" from the time when the solar system was formed. It also consists of frozen volatiles (termed "ices"), such as "methane, ammonia, and water".
<u>Relationship to dwarf planets:</u>
This belt is also a home to the dwarf planets such as "Pluto, Haumea, and Makemake".
Tell the teacher, do NOT clean it up yourself.