Element X has two isotopes. X-15 has 7 protons and 8 neutrons. What is the atomic number and mass number of the second isotope, which has 10 neutrons in its nucleus?
The most important thing to keep in mind here is that isotopes are atoms that have the same number of protons inside their nuclei.
In other words, an isotope is defined as an atom that shares the number of protons with at least one other atom but differs in the number of neutrons it has inside its nucleus.
In this case, you know that element
Now, the name of the isotope is written using its mass number, which is simply the number of protons and neutrons located inside the nucleus.
The second isotope is said to contain
#A = "7 protons" + "10 neutrons" = 17#
This means that the second isotope will be called