In hydrogen atom, transition from the state $\mathrm{n}=6$ to $n=1$ results in ultraviolet radiation. Infrared radiation will be obtained in the transition
A radioactive element ${ }_{92}^{242} \mathrm{X}$ emits two $\alpha$ particles, one electron and two positrons. The product nucleus is represented by ${ }_{\mathrm{p}}^{234} \mathrm{Y}$. The value of $P$ is
The activity of radioactive sample is measured as $\mathrm{N}_0$ counts per minute at time $\mathrm{t}=0$, and $\frac{\mathrm{N}_0}{\mathrm{e}}$ counts per minute at time $\mathrm{t}=3$ minute, The activity reduces to half its value in time (in minute)
In hydrogen atom, the energy of electron in first and third orbit is ' $E_1$ ' and' $E_3$ ' respectively. If $E_3=x E_1$ then the value of $x$ will be