Consider the following two statements

$A.$ Energy spectrum of $\alpha-$ particles emitted in radioactive decay is discrete

$B.$ Energy spectrum of $ \beta -$ particles emitted in radioactive decay is continuous

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?

In the nuclear reaction: $X(n,\,\alpha ){\,_3}L{i^7}$ the term $X$ will be 

The number of $\alpha$ and $\beta ^-$ emitted during the radioactive decay chain starting from ${}_{88}^{226}Ra$ and ending at ${}_{82}^{206}Pb$ is

${ }_{82}^{290} X \xrightarrow{\alpha} Y \xrightarrow{e^{+}} Z \xrightarrow{\beta^{-}} P \xrightarrow{e^{-}} Q$

In the nuclear emission stated above, the mass number and atomic number of the product $Q$ respectively, are

Alpha particles are