Schematic representation of three atoms X, Y and Z is given as

Which of the following statements is/are correct ?

I) X, Y and Z are isotopes

II) X and Z have the same valency

III) The increasing order of atomic numbers is  $\text{X}<\text{Z}<\text{Y}$

IV) X, Y and Z have stable electronic configurations.

The given information is X, Y and Z are three chemical elements.

They have different electronic configuration as shown in the below diagram.

According to Bohr and Burry rules for the electronic configuration of elements K shell is filled with electrons first and then L shell, N shell…

Therefore, the element Y has greater atomic number than X and Z. In the given all elements X has small atomic number. Hence, the increasing order of atomic number of X, Y and Z is $\text{X}<\text{Z}<\text{Y}$.

Based on the valency electrons, the elements X and Z have same valency ($1,8-7=1$).