Hey there!:
Mass = 21.09 g
Volume = 6.44 mL
Therefore;
Density = mass / Volume
Density = 21.09 / 6.44
Density = 3.274 g/mL
<span>261 million kilometers</span>
3rd one:
it is very reactive because it does not have a full Valence shell.
this is because it's in group 1 so it has one electron in its outer shell, and it wants to have a full outer shell ( which it can gain by losing the electron in a reaction).
Hope this helps :)
