In gold foil experiment number of deflected $\alpha -$ particles at angle $90^o$ is $63$ than number of $\alpha -$ particle deflected at $120^o$ is

The wavelength of the first line of Balmer series of hydrogen atom is $\lambda \,\mathop A\limits^o $. The wavelength of this line of a double ionised lithium atom $(Z = 3)$is

Choose the correct alternative from the clues given at the end of the each statement:

$(a)$ The size of the atom in Thomson’s model is .......... the atomic size in Rutherford’s model. (much greater than/no different from/much less than.)

$(b)$ In the ground state of .......... electrons are in stable equilibrium, while in .......... electrons always experience a net force. (Thomson’s model/ Rutherford’s model.)

$(c)$ A classical atom based on .......... is doomed to collapse. (Thomson’s model/ Rutherford’s model.)

$(d)$ An atom has a nearly continuous mass distribution in a .......... but has a highly non-uniform mass distribution in .......... (Thomson’s model/ Rutherford’s model.)

$(e)$ The positively charged part of the atom possesses most of the mass in .......... (Rutherford’s model/both the models.)

The ratio of the speed of the electrons in the ground state of hydrogen to the speed of  light in vacuum is

Apply Bohr’s atomic model to a lithium atom. Assuming that its two $K$-shell electrons are too close to nucleus such that nucleus and $K$-shell electron act as a nucleus of effective positive charge equivalent to electron. The ionization energy of its outermost electron is......$eV$

Explain Rutherford's explanation for scattered $\alpha $ -particles.