For the Paschen series,the values of $n_1$ and $n_2$ in the expression $\Delta E = R h c \left( \frac{1}{n_1^2} - \frac{1}{n_2^2} \right)$ are:

The masses of photons corresponding to the first lines of Lyman and Balmer series of the spectrum of hydrogen atom are in the ratio of

From the following energy levels of a hydrogen atom,the values of $E_{\infty}$ and $E_3$ in $J$ are,respectively: $E_{\infty} = \ldots \ldots \ldots$ $E_3 = \ldots \ldots \ldots$ Given: $E_2 = -0.545 \times 10^{-18} \ J$,$E_1 = -2.18 \times 10^{-18} \ J$.

When a metal surface is irradiated with light of frequency $x \ Hz$,the kinetic energy of emitted photoelectrons is $z \ J$. When the same metal is irradiated with light of frequency $y \ Hz$,the kinetic energy of emitted electrons is $\frac{z}{3} \ J$. What is the threshold frequency (in $Hz$) of the metal?

When atoms are bombarded with alpha particles,only a few in a million suffer deflection,while others pass through undeflected. This is because:

The emission spectrum of a gaseous atom is line-based and not continuous. Why?