Question

I don't know how to do this, pls help!

Answer 1

Cations from smallest to largest
Li⁺ ,Na⁺, K⁺ (from Periodic Table, the bigger number of period, the bigger size, of atom, so the bigger size of cation)

1) LiF smaller  cation then KF
1,036                                 853
The lattice energy increases as cations get smaller, as shown by LiF and KF.
I think this one should be correct answer, because the compared substances have also the same anion, and we can compare cations in them.

2) The same cation Li , so wrong statement.

3)The same cation Na , so wrong statement.

4) NaCl smaller cation then KF
  786                                   853

Answer 2

its A ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,