Would it be easier to crystallize polytetrafluoroethylene (teflon) (c2f4) or polystyrene (cshs)? why?

Crystallization of tetrafloroethane C₂F₄ is easier than styrene C₈H₈ .

Explanation:  

Crystallization -

crystallization is a process in which atoms are restructured in the form of crystals , some of the ways by which crystals form are melting , precipitating from a solution.

we need to consider the melting point of the given compounds ,  

the melting point of styrene C₈H₈ is -30 °C

whereas the melting point of tetrafloroethane C₂F₄ is -140 °C ( 130.7 K ) since the melting point of C₂F₄ is less than C₈H₈ so it is easy to melt C₂F₄.  

Hence it is easier to crystallize C₂F₄ .

your parents i think this could be it

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.