Which of the following sets of nuclei represents a triad of isotones?

$_{35}X^{88}$ is an unstable isotope,which decays in two successive steps to produce the stable isotope $_{32}Z^{84}$ as $_{35}X^{88}$ $\xrightarrow{I} Y$ $\xrightarrow{II} _{32}Z^{84}$. The correct statement is (possible emissions are $\alpha, \beta^-$,positron,neutron,and $_1H^1$,and in each step only one particle is involved).

$X$ $\xrightarrow{-\alpha } Y$ $\xrightarrow{-\beta } Z$ $\xrightarrow{-\beta } W$
In the above sequence of reaction,the elements which are isotopes of each other are

The isotone of $_{32}Ge^{76}$ is:

Relative abundance (in percentage) of ${}^{14}C$ isotope is

Which radioactive carbon isotope has been helpful in understanding the mechanism of photosynthesis in plants?