Answer:
The first option A (one electron)
Step-by-step explanation:
From the left side of the arrow, Fr has a mass number of 223 and an atomic number of 87, so we want both of the numbers to be the same on the right side.
On the right side, Rn has a mass number of 223, which is the same on the left side for Fn, so we do not need to add any more to the mass number, hence 0.
Rn has an atomic number of 86, but Fr has an atomic number of 87, so we need one more electron to make both sides equal.