Um átomo X possui 8 neutrons e seu número atômico e igual a 8. Sabendo que esse atomo é isótopos de Y, que possui número de massa 18, responda: Qual o numero de nêutrons do atomo Y?

Question in English:

An atom X has 8 neutrons and its atomic number equals 8. Knowing that this atom is isotopes of Y, which has mass number 18, answer: What is the number of neutrons in atom Y?

Answer:

Isotopes are defined as the atoms which have same number of protons but different number of neutrons of same element. Since the proton number is same, the atomic number also same. Hence the atomic number of Y is 8.

Mass number = atomic number + neutron number

18 = 8 + neutron number

Neutron number = 10

Hence, there are 10 neutrons in Y.