Originally the radioactive beta decay was thought as a decay of a nucleus with the emission of electrons only (Case $I$) . However, in addition to the electron, another (nearly) massless and electrically neutral particle is also emitted (Case $II$). Based on the figure below, which of the following is correct?
$(a)$ in both cases $I$ and $II$
$(a)$ in case $I$ and $(b)$ in case $II$
$(a)$ in case $II$ and $(b)$ in case $I$
$(b)$ in both cases $I$ and $II$
A nucleus of an element ${}_{84}{X^{202}}$ emits an $\alpha $-particle first, $\beta $ -particle next and then a gamma photon. The final nucleus formed has an atomic number
When a $_4B{e^9}$ atom is bombarded with $\alpha - $ particles, one of the product of nuclear transmutation is $_6{C^{12}}$. The other is
The total number of $\alpha$ and $\beta$ particles emitted in the nuclear reaction ${ }_{92}^{238} \mathrm{U} \rightarrow{ }_{82}^{214} \mathrm{~Pb}$ is
A free neutron decays into a proton, an electron and
In nuclear reaction $_2H{e^4}{ + _z}{X^A}{ \to _{z + 2}}{Y^{A + 3}} + A,\;A$ denotes