The average atomic mass of a sample of an element $X$ is $16.2 \, u$. What are the percentages of isotopes $_8^{16}X$ and $_8^{18}X$ in the sample (in $\%$)?

Summarize the rules for writing the distribution of electrons in various shells for the first eighteen elements.

Compare the properties of electrons,protons,and neutrons.

For the following statements,write $T$ for True and $F$ for False.
$(a)$ $J$.$J$. Thomson proposed that the nucleus of an atom contains only nucleons.
$(b)$ $A$ neutron is formed by an electron and a proton combining together. Therefore,it is neutral.
$(c)$ The mass of an electron is about $\frac{1}{2000}$ times that of a proton.
$(d)$ An isotope of iodine is used for making tincture iodine,which is used as a medicine.

Rutherford's alpha-particle scattering experiment was responsible for the discovery of

Complete the following table.

Atomic Number	Mass Number	Number of Neutrons	Number of Protons	Number of Electrons	Name of the Atomic Species
$9$	-	$10$	-	-	-
$16$	$32$	-	-	-	sulphur
-	$24$	-	$12$	-	-
-	$2$	-	$1$	-	-
-	$1$	$0$	$1$	$0$	-