What is the mass number of an isotope that has 2 neurons?

We all know that from the periodic table, an element with two neutrons has two protons and mass number is number of neutrons + no of protons.

Therefore, the mass number is 4.

An isotope means that there are a different number of neutrons and protons, so if there are two neutrons it means that there is only one proton. That means the mass would be 3.

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