Pick out the correct answer:
1. A radioactive nucleus \(_{A}X^Z\) undergoes spontaneous decay in the sequence,
\(_{A}X^Z\) \(\rightarrow\) \(_{Z-1}B\) \(\rightarrow\) \(_{Z-3}C\) \(\rightarrow\) \(_{Z-2}D\)
where \(Z\) is the atomic number of element \(X\). The possible decay particles in the sequence are __________. [NEET 2021]
\(_{A}X^Z\) \(\rightarrow\) \(_{Z-1}B\) \(\rightarrow\) \(_{Z-3}C\) \(\rightarrow\) \(_{Z-2}D\)
where \(Z\) is the atomic number of element \(X\). The possible decay particles in the sequence are __________. [NEET 2021]
2. The half-life of a radioactive isotope \(X\) is \(20\ yr\). It decays to another element \(Y\) which is stable. The two elements \(X\) and \(Y\) were found to be in the ratio \(1\ : 7\) in a sample of a given rock. The age of the rock is estimated to be __________. [NEET 2013]