Sncl2 is solid while sncl4 is liquid

As the oxidation state of a metal increases, its electronegativity increases and the bonds become increasingly covalent. SnCl2 forms a network solid where the atoms are bonded to one another throughout a network of polar covalent bonds. SnCl4 is molecular, and held together by weaker intermolecular forces called London dispersion forces. 

The answer is b

8.24 kpa.

solution:

(7.25 kpa) x (60.0 + 273.15) / (20.0 + 273.15)
  = 8.24 kpa