If a nucleus $P$ converts into a nucleus $Q$ by the decay of one alpha particle and two $\beta^{-}$particles, then the nuclei $P$ and $Q$ are

The phenomenon of physics that deals with the constitution and structure of matter at the minute scales of atoms and nuclei is

The ratio of wavelengths of second line in Balmer series and the first line in Lyman series of hydrogen atom is

A radioactive material of half-life 2.5 hours emits radiation that is 32 times the safe maximum level. The time (in hours) after which the material can be handled safely is