Question:
In the Gold foil experiment of Geiger and Marsden, that paved the way for Rutherfords model of an atom, $1.00 \%$ of the a-particles were found to deflect at angles $>50^{\circ}$. If one mole of a-particles were bombarded on the gold foil, compute the number of a-particles that would deflect at angles less than $50^{\circ}$.
Solution:
Percentage $(\%)$ of particles deflected at an angle more than $50^{\circ}=1 \%$
Percentage $(\%)$ of a-particles deflected at an angle less than $50^{\circ}=100-1=99 \%$
Moles of $\alpha$-particles which bombarded the given gold foil $=1 \mathrm{~mol}$ or $6.022 \times 10^{23}$ particles
No. of $\alpha$-particles deflected at an angle less than $50^{\circ}=\frac{6.022 \times 10^{23} \times 99}{100}=5.96 \times 10^{23}$.