In the Rutherford experiment,for a head-on collision of $\alpha$-particles with a gold nucleus,the impact parameter is:

State and explain Dalton's atomic theory.

What is the impact parameter?

An alpha particle of energy $K \text{ MeV}$ is moving towards a nucleus of atomic number $Z$. The distance of closest approach of the alpha particle to the nucleus in metres is

In an alpha particle scattering experiment,the distance of closest approach for the $\alpha$-particle is $4.5 \times 10^{-14} \ m$. If the target nucleus has an atomic number $Z = 80$,then the maximum velocity of the $\alpha$-particle is approximately $... \times 10^5 \ m/s$.
$\left(\frac{1}{4 \pi \epsilon_0} = 9 \times 10^9 \ SI \ unit, \text{mass of } \alpha \text{-particle } m = 6.72 \times 10^{-27} \ kg, e = 1.6 \times 10^{-19} \ C\right)$

In the gold foil experiment,the number of deflected $\alpha$-particles at an angle of $90^o$ is $63$. What is the number of $\alpha$-particles deflected at $120^o$?