During negative $\beta$-decay,which of the following processes occurs?

$_{86}A^{222} \to _{84}B^{210}$. In this reaction,how many $\alpha$ and $\beta$ particles are emitted?

In a radioactive sample,${ }_{19}^{40} K$ nuclei decay into stable ${ }_{20}^{40} Ca$ nuclei with a decay constant of $4.5 \times 10^{-10} \text{ per year}$ or into stable ${ }_{18}^{40} Ar$ nuclei with a decay constant of $0.5 \times 10^{-10} \text{ per year}$. Given that in this sample,all the stable ${ }_{20}^{40} Ca$ and ${ }_{18}^{40} Ar$ nuclei are produced by the ${ }_{19}^{40} K$ nuclei only. In time $t \times 10^9 \text{ years}$,if the ratio of the sum of stable ${ }_{20}^{40} Ca$ and ${ }_{18}^{40} Ar$ nuclei to the radioactive ${ }_{19}^{40} K$ nuclei is $99$,the value of $t$ will be: [Given $\ln 10 = 2.3$]

In the nuclear decay sequence given below:
$_Z{X^A} \to {}_{Z + 1}{Y^A} \to {}_{Z - 1}{K^{A - 4}} \to {}_{Z - 1}{K^{A - 4}}$
the particles emitted in the sequence are:

Radioactivity was discovered by

The particles emitted by radioactive decay that are deflected by a magnetic field are: