Why is the lattice energy of potassium bromide more exothermic than the lattice energy of rubidium iodide?

Rubidium iodide has a lattice energy of -617 kJ⋅mol−1, while potassium bromide has a lattice energy of -671 kJ⋅mol−1.

Use the following terms to fill in the blanks of the sentences below...

potassium

below

less more

get much closer to each other then

bromine

smaller

larger

above

do not release as much

release much more

cannot get as close to each other as

iodine

1. Rubidium is _____  _______ on the periodic table and is below _____  on the periodic table.

2. Therefore, both the rubidium ion and the iodide ion are ______  than the potassium ion and the bromide ion.

3. So, the rubidium ion and the iodide ion ______ the potassium ion and the bromide ion, therefore, they ______ energy and the lattice energy of potassium bromide is ______   exothermic.

Thank you in advance, we haven't learned this yet and it's due tomorrow :(