The crystal structure of $NaCl$ is:

$A$ neon sign does not produce

$A$ hydrogen atom emits a photon corresponding to an electron transition from $n = 5$ to $n = 1$. The recoil speed of the hydrogen atom is almost......$m/s$ (mass of proton $\approx 1.6 \times 10^{-27} \ kg$).

In a Franck-Hertz experiment,an electron of energy $5.6 \ eV$ passes through mercury vapour and emerges with an energy $0.7 \ eV$. The minimum wavelength of photons emitted by mercury atoms is close to ............. $nm$.

An electron of a stationary hydrogen atom transitions from the fifth energy level to the ground level. The velocity that the atom acquires as a result of photon emission will be:

The band spectra (characteristic of molecular species) is due to emission of radiation from which state of matter?