Which of the following is not conserved in nuclear reaction ? 

The fossil bone has${\mathrm{a}}^{14}\mathrm{C}:{}^{12}\mathrm{Cratio}$, which is $\left(\frac{1}{16}\right)$ of that in a living animal bone. If the half-life of ${}^{14}\mathrm{C}$ is $5730\mathrm{yr}$, then the age of the fossil is

A radioactive nucleus (initial mass number $A$ and atomic number $Z$ ) emits $3\alpha$ -particles and$2$ positrons. The ratio of number of neutron to that of protons in the final nucleus will be

A radioactive nucleus $A$ finally transforms into a stable nucleus $B$. Then $A$ and $B$ can be.