State whether the following statement is true or false:
One atomic mass unit is a mass unit equal to exactly one-twelfth $(1/12)$ the mass of one atom of carbon-$12$.

The electronic configuration of an element $X$ is $2, 8, 2$.
$(a)$ Find the number of electrons present in the atom of element $X$.
$(b)$ Write the atomic number.
$(c)$ Is this element $X$ a metal or a non-metal?
$(d)$ Find out the valency of the element $X$.

Write the conclusions drawn by Rutherford for the following observations during his $\alpha$-scattering experiment:
$(a)$ Most of the alpha particles passed straight through the gold foil.
$(b)$ Some alpha particles got deflected from their path.
$(c)$ $A$ very small fraction of alpha particles got deflected by $180^{\circ}$.

State whether the following statement is true or false:
Atomic radius is measured in nanometres. $1 \, m = 10^9 \, nm$.

$(a)$ How many neutrons are present in $C-14$ isotope of carbon?
$(b)$ How many protons does $He^{2+}$ ion possess?
$(c)$ How many maximum electrons can be filled in the $3^{rd}$ orbit of an atom?
$(d)$ How many electrons does $He^{2+}$ ion possess?

With the help of a labelled diagram,describe in brief the Rutherford's alpha particle scattering experiment. Write any three important conclusions drawn from the experiment.