Answer:
A
Explanation:
calcium
rubidium
strontium
The element which has an electron configuration of [Kr] 5s² is calcium .
It is defined as a substance which cannot be broken down further into any other substance. Each element is made up of its own type of atom. Due to this reason all elements are different from one another.
Elements can be classified as metals and non-metals. Metals are shiny and conduct electricity and are all solids at room temperature except mercury. Non-metals do not conduct electricity and are mostly gases at room temperature except carbon and sulfur.
The number of protons in the nucleus is the defining property of an element and is related to the atomic number.All atoms with sameatomic numberare atoms of same element.
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the given element is
¹³⁰₅₅Cs
the superscript - 130 is the atomic mass / mass number
mass number is the sum of protons and neutrons
subscript - 55 is the atomic number
atomic number is the number of protons
therefore we can write the following equations
protons = 55
protons + neutrons = 130
so neutrons = 130 - protons
nuetrons = 130 - 55 = 75
number of neutrons = 75