Answer
a.
potassium-39: $^{39}_{19}K$
potassium-40: $^{40}_{19}K$
potassium-41: $^{41}_{19}K$
b.
The three isotopes have the same atomic number, and thus, the same symbol, number of protons and electrons. But, their atomic masses are completely different.
Work Step by Step
a.
1. Identify the symbol for potassium:
It is $K$
2. Find its atomic number using a periodic table, it goes subscript on the left of the symbol.
19: $_{19}K$
3. The number after the name of the element represents its atomic mass, and it goes superscript on the left of the symbol.
potassium-39: $^{39}_{19}K$
potassium-40: $^{40}_{19}K$
potassium-41: $^{41}_{19}K$
b. Isotopes have the same number of protons, and thus, they all have to be the same element, with the same symbol. And what differs them is their atomic masses.
