A certain stable nucleide, after absorbing a neutron, emits $\beta$-particle and the new nucleide splits spontaneously into two $\alpha$-particles. The nucleide is
${ }_2^4 He$
${ }_3^7 Li$
${ }_4^6 Be$
${ }_3^6 Li$
Some radioactive nucleus may emit
${ }_{92}^{238} U$ atom disintegrates to ${ }_{84}^{214} Po$ with a half of $45 \times 10^9$ years by emitting $\operatorname{six} \alpha-$ particles and $n$ electrons. Here, $n$ is
A nucleus of an element $_{84}{X^{202}}$ emits an $\alpha-$ particle first, a $\beta-$ particle next and then a gamma photon. The final nucleus formed has an atomic number
The nucleus $_{48}^{115}Cd$ after two successive ${\beta ^ - }$ decays will give
The electron emitted in beta radiation originates from