$1 \text{ Curie}$ is equal to

In the uranium radioactive series, the initial nucleus ${}^{238}_{92}U$ decays to the final nucleus ${}^{206}_{82}Pb$. In this process, the number of $\alpha$-particles and $\beta$-particles emitted are:

Assertion: Cobalt-$60$ is useful in cancer therapy.
Reason: Cobalt-$60$ is a source of $\gamma$-radiations capable of killing cancerous cells.

If a nucleus emits an $e^-$ particle,then its neutron-to-proton ratio $[n/p]$ will .....

Outside a nucleus,which of the following statements is true?

Explain $\beta$-decay and how a radioactive nucleus emits $\beta$-particles,even if there are no $\beta$-particles in the nucleus. Why does the mass number of the radioactive nuclide not change during $\beta$-emission?