The half-life period of a ratio-active element $$X$$ is same as the mean life time of another ratio-active element $$Y.$$ Initially they have the same number of atoms. Then

Which of the following transitions in hydrogen atoms emit photons of highest frequency ?

The energy spectrum of $$\beta $$-particles [ number $$N(E)$$ as a function of $$\beta $$-energy $$E$$ ] emitted from a radioactive source is

The $$'rad'$$ is the correct unit used to report the measurement of