Question

In the alpha decay of Francium-221, what daughter element is produced? (You may need to refer to the periodic table in the lesson.)

Answer 1

In an alpha decay, the original nucleus decays into a daughter nucleus + an alpha particle, which consists of 2 protons and 2 neutrons.
The atomic number (number of protons) of the Francium is 87, and since in the decay it loses 2 protons, the atomic number of the daughter nucleus should be 85. Looking at the periodic table ,this corresponds to Astatine, and therefore this is the element produced in the alpha decay of Francium-221.
Moreover, the mass number (number of protons+neutrons) decreases by 4 (because an alpha particle carries 2 protons+2 neutrons), therefore in the reaction the mass number will decrease from 221 to 217. 
So, the daughter element is astatine-217.

Answer 2

217   AT

 85      (i don't have enough characters so ignore this part)