What is the atomic number and mass number of an atom when an α (alpha) particle is emitted?

When an α (alpha) particle is emitted by an atom, its atomic number (Z) decreases by 2 and mass number (A) decreases by 4.

Here P is called the parent nucleus.
D is called as daughter nucleus.

In the above example Uranium is the parent nucleus and thorium is the daughter nucleus.

Rutherford and Soddy’s law of α emission states that “whenever an α particle is emitted from a radioactive nucleus, the atomic number decreases by 2 and the mass number decreases by 4 and the position of the element shifts by two places to left in the periodic table”.