Question for Decay

[stephen]

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A radioactive sample, initially consists of
only nuclide X, decays by the emission of
an alpha particle to form a stable daughter
nuclide Y. Which of the following
quantities will decrease with time?
(1) The rate of decay of nuclide X.
(2) The rate of growth of nuclide Y.
(3) The rate of emission of alpha
particles.


What's the meaning of rate of growth of nuclide Y?