Question

What is the mass number and the atomic number of Boron $-11$ ?

Answer 1

We know that the isotope of a particular element can be defined as the element having the same atomic number but different atomic mass. In other words, we can say that isotopes have the same number of protons but they differ in the number of neutrons.

Complete answer:
We can define the atomic number or proton number of a compound component as the quantity of protons found in the core of each atom of that component. The atomic number remarkably recognizes a chemical component. It is indistinguishable from the charge number of the core. In an uncharged molecule, the atomic number is additionally equivalent to the quantity of electrons. In these types of questions, where we have to calculate the percentage abundance of the isotopes of an element, we have to take the atomic mass of their isotopes.
In case, we have only two isotopes, we can take the percentage of one isotope as x and other as $1-x.$ We know that the number of protons in Boron is five and the number of electrons in Boron is five. So, we saw that the atomic number is the quantity of protons found in the nucleus. In boron, the nucleus has five protons. So, we can say that the atomic number of boron is five. Boron is a metalloid that means it has the intermediate properties of metals and non - metals both and it comes under the category of p-block elements. The name boron $-11$ is used to designate an isotope of boron that has a mass number equal to $11.$ Boron, B, which is located in period two, group $13$ of the periodic table has an atomic number equal to $5.$ Therefore, the mass number of this boron isotope is equal to $11$ and the atomic number to $5.$

Note:
Remember that the number of electrons is always equal to the atomic number of an atom only in the neutral state, but whenever an atom is present in the form of ion then the number of electrons varies from the atomic number.