Will $^{35}Cl$ and $^{37}Cl$ have different valencies? Justify your answer.

$(a)$ Explain why did Rutherford select a gold foil in his alpha scattering experiments?
$(b)$ What observations in $\alpha$-scattering experiment led Rutherford to make the following conclusions?
$(i)$ Most of the space in an atom is empty.
$(ii)$ Nucleus is positively charged.
$(c)$ Mention any two drawbacks of Rutherford's model.

Which of the following statements about Rutherford's model of the atom are correct?

Which of the following statements is always correct?

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-$12$.

Find the number of electrons,protons,and neutrons possessed by the alpha particles $\left({ }_{2}^{4} He ^{2+}\right)$ used in the gold leaf experiment.