The Rutherford $\alpha$-particle experiment shows that most of the $\alpha$-particles pass through almost unscattered while some are scattered through large angles. What information does it give about the structure of the atom?

Assertion $(A)$: The impact parameter for $\alpha$-particles scattered by $180^{\circ}$ is zero.
Reason $(R)$: Zero impact parameter means that the $\alpha$-particles tend to hit the centre of the nucleus.

An alpha particle is accelerated through a potential difference of $10^6 \ V$. Its kinetic energy will be $MeV$.

$A$ proton is fired from very far away towards a nucleus with charge $Q=120 \ e$,where $e$ is the electronic charge. It makes a closest approach of $10 \ fm$ to the nucleus. The de Broglie wavelength (in units of $fm$) of the proton at its start is: (take the proton mass,$m_0 = (5/3) \times 10^{-27} \ kg$,$h/e = 4.2 \times 10^{-15} \ J \cdot s/C$,$\frac{1}{4 \pi \varepsilon_0} = 9 \times 10^9 \ N \cdot m^2/C^2$,$1 \ fm = 10^{-15} \ m$)

In the Rutherford experiment,$\alpha -$ particles are scattered from a nucleus as shown. Out of the four paths,which path is not possible?

State the postulates of Dalton's atomic theory.