A radioactive element, $\mathrm{X}$, decays by the sequence and with half lives, given below:
$$
\begin{array}{ll}
\mathrm{X}\left(\mathrm{t}_{12}=30 \mathrm{~min}\right) & \stackrel{\lambda_{1}}{\longrightarrow} \mathrm{Y}+\alpha \\
\mathrm{Y}\left(\mathrm{t}_{12}=2 \text { days }\right) & \stackrel{\lambda_{2}}{\longrightarrow} \mathrm{Z}+2 \beta
\end{array}
$$
Which of the following statement(s) is/are incorrect?
(a) Atomic numbers of $\mathrm{X}$ and $Z$ are same
(b) Disintegration constant $\lambda_{2}>\lambda_{1}$
(c) The mass number of $\mathrm{Y}$ is greater than that of $\mathrm{X}$.
(d) $\mathrm{Y}$ and $Z$ are isotopes.