Which of the following does not contain material particles?

Fill in the blank: Wave number is measured in units of .........

The velocity of $\alpha-$rays is approximately

Which of the following is not deflected by a magnetic field?

$A$ gas absorbs a photon of $355 \ nm$ and emits at two wavelengths. If one of the emissions is at $680 \ nm,$ the other is at : ................. $nm$

Work functions of four metals $M_1, M_2, M_3$ and $M_4$ are $4.8, 4.3, 4.75$ and $3.75 \ eV$ respectively. The metals which do not show photoelectric effect when light of wavelength $310 \ nm$ falls on the metals are