Question

The letters X, Y and Z represent different atoms.
${}_{19}^{40}X$ ${}_{19}^{39}Y$ ${}_{20}^{40}Z$
What can be deducted from the proton and nucleon numbers of X, Y and Z?
A.X and Y are the same elements
B.X and Z are the same elements
C.X has more protons than Y
D.Z has more neutrons than Y

Answer 1

Hint: Before attempting this question, one should have prior knowledge about the concept of atoms and the atomic number also remember that atoms of the same element can have different mass numbers but their atomic number will not change, use this information to approach the solution.

Complete answer:
According to the given information we know that X, Y and Z are different atoms
It is given that X element have atomic number 19 and mass number 40 so it means it consist of 19 electrons, 19 protons and 21 neutrons
For Y atomic number is given as 19 and mass number is 39 so it has 19 electrons, 19 protons and 20 neutrons
But in case of Z it has atomic number 20 and mass number 40 which means it have 20 electrons, 20 protons and 20 neutrons
Now we know that elements which have same atomic number but different mass number are same elements and since X and Y have same atomic number but different mass number
Therefore, X and Y are the same elements

Hence, option A is the correct option.

Note:
In the above solution we used the given information which concluded that X and Y were the same elements but we also knew that since they have number of electrons and protons but different numbers of neutrons which tell that they are different isotopes but in order to come to this result we find the number of electrons, protons and neutrons where we knew that number of electron and number of proton is equal to the atomic number of element whereas number of neutrons is equal to mass number – atomic number.