An ion $X^{2-}$ contains $10$ electrons and $8$ neutrons. What are the atomic number and mass number of element $X$?

Which of the following statements is always correct?

Rutherford's alpha $(\alpha)$ particles scattering experiment resulted in the discovery of:

State whether the following statement is true or false:
Each isotope of an element is an impure substance.

Atomic models have been improved over the years. Arrange the following atomic models in their chronological order:
$(i)$ Rutherford's atomic model
$(ii)$ Thomson's atomic model
$(iii)$ Bohr's atomic model

The following data represents the distribution of electrons,protons,and neutrons in atoms of four elements $A, B, C, D.$

Element	Protons,Neutrons,Electrons
$A$	$9, 10, 9$
$B$	$16, 16, 16$
$C$	$12, 12, 12$
$D$	$17, 22, 17$

Answer the following questions:
$(a)$ Give the electronic distribution of element $B.$
$(b)$ The valency of element $A$.
$(c)$ The atomic number of element $B.$
$(d)$ The mass number of element $D$.