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.

In $1911$,the physicist Ernest Rutherford discovered that atoms have a tiny,dense nucleus by shooting positively charged particles at a very thin gold foil. $A$ key physical property which led Rutherford to use gold was that it was

An $\alpha$-particle of energy $5 \text{ MeV}$ is moving forward for a head-on collision. The distance of closest approach from the nucleus of atomic number $Z=50$ is . . . . . . $\times 10^{-14} \text{ m}$.
$(k=9 \times 10^{9} \text{ SI}, e=1.6 \times 10^{-19} \text{ C}, 1 \text{ eV}=1.6 \times 10^{-19} \text{ J})$

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

What is the plum pudding model of the atom?