Question 10

It increases going left to right along a period, and decreases going top to bottom down a group.

Both patterns follow from the same thing — how strongly the nucleus holds the outer electrons. Down a group those electrons are further away, so the atom both gives up its own electron more easily and pulls another atom's electrons less strongly. Check it: across period 3, Na 0.9 up to Cl 3.0; down group I, Li 1.0 to K 0.8.