Answer:
Groups like the Halogens, which include Chlorine and Flourine, share similar properties both behaviorally and structurally. The Periodic Table is essentially a bunch of patterns and trends and the groups (like the one with Sodium and Potassium) were grouped together because of these similarities.
Explanation:
https://en.wikipedia.org/wiki/Alkali_metal
273g/25 mL = 10.92 (that's the density)
What has a density of 10.92 grams/mL? I don't know but I bet it's in your notes or on the worksheet.
Answer:
Here's what I find.
Explanation:



The sign of ΔH changes when you reverse the reaction.
I think the charge is +2
Hope this helps