When an alpha particle is emitted from an unstable nucleus, what happens to the atomic number of the nucleus?a) The atomic number decreases by 4.b) The atomic number increases by 2.c) The atomic number increases by 4.d) The atomic number decreases by 2.e) The atomic number remains constant.

d) The atomic number decreases by 2

Explanation:

A particle alpha is He(2+)

Where we have:

A = 4

Z =  2

The atomic number, the number of protons, must be conserved:

At the beginning (before the emission) we have Z protons.

After the emission, we will have an element with an atomic number X , and an alpha particle with an atomic number = 2.

Then the total number of protons after the emission is X + 2.

The conservation equation is:

Z = X + 2

Isolating X we get:

X = Z - 2

Then after the emission, the atomic number is decreased by 2.

The correct option will be:

d) The atomic number decreases by 2