Write down the electron distribution of chlorine atom. How many electrons are there in the $L$ shell? (Atomic number of chlorine is $17$).

$(a)$ What are canal rays? Who discovered them? What is the charge and mass of canal rays?
$(b)$ How are the canal rays different from electrons in terms of charge and mass?

Write two differences between isobars and isotopes.

$(a)$ Which of the following electronic configurations are not possible? Give reasons.
$(i)$ $X: 2, 8, 4$
$(ii)$ $Y: 3, 8, 2$
$(iii)$ $Z: 2, 8, 9$
$(b)$ Write electronic configurations of the following elements and predict their valencies:
Fluorine: $9$,Aluminium: $13$,Argon: $18$

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 $D$.

Calculate the number of neutrons present in the nucleus of an element $X$ which is represented as $^{31}_{15}X$.