f.4 chem

I think the answer is C

I absolutely sure that astatine is a solid at room temperature and preesure because the reactivity of group VII elements decreases down the group, and the reactivity also decreases down from gas to solid as the van der Waal's force between gases is weak and the total surface area of gas is large. Moreover, there is only a liquid in group VII, that is bromine, so I could confirm that (1) is correct.

For (3), I am sorry that I am not sure. Since the similarities of group VII elements are reactive, I think that it could react with potassium to form a salt,potassium astatide,KAt.
However, this experiment may be too dangerous as both potassium and astatine are reactive elements.

I am poor at Chem, so I just hope that my answer could help you for reference only.