An atom with $3$ protons and $4$ neutrons will have a valency of:

The isotope of uranium used as a fuel in nuclear reactors and carbon used in radiocarbon dating are

The ion of an element has $3$ positive charges. The mass number of the atom is $27$ and the number of neutrons is $14$. What is the number of electrons in the ion?

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

$(a)$ How many neutrons are present in $C-14$ isotope of carbon?
$(b)$ How many protons does $He^{2+}$ ion possess?
$(c)$ How many maximum electrons can be filled in the $3^{rd}$ orbit of an atom?
$(d)$ How many electrons does $He^{2+}$ ion possess?

$(a)$ Why did Rutherford choose gold and not any other lighter element (such as aluminium) for his experiment? Explain your answer giving two reasons.
$(b)$ Write the name and symbol of the particle chosen by Rutherford for bombardment against the gold foil in his experiment.