Which has the least penetrating power?

$A$ radioactive nuclide $X$ decays at the rate of $1.00 \times 10^5 \ disintegration \ s^{-1} \ g^{-1}$. Radium decays at the rate of $3.70 \times 10^{10} \ disintegration \ s^{-1} \ g^{-1}$. The activity of $X$ in millicuries $g^{-1}$ $(mCi \ g^{-1})$ is

$A$ radioactive nucleus will not emit

How many alpha particles are emitted in the nuclear transformation
$_{84}Po^{215} \xrightarrow{} _{82}Pb^{211}$?

In the following nuclear reaction,identify $x$: $_{29}Cu^{64} \to _{28}Ni^{64} + x$

If a radioactive isotope with atomic number $A$ and mass number $M$ emits an $\alpha$-particle,the atomic number and mass number of that new isotope will become: