Question

why do we see vapor when we breath out in winter????

Answer 1

when we breath out in winter water vapour is also released with CO2.this water vapour, when comes in contact with cold and humid air ,which cannot hold water anymore,  condences  and hence it forms minute droplets which we see like fog.
     think its the correct ans. :)

Answer 2

It's  due  to  condensation.In  winter  it's   cold  outside.We  inhale  oxygen  and  exhale  carbon  dioxide.Our  breath  also  contains  a  little  bit  of  moisture  .  It's   because  our  mouth  and  lungs  are  moist.For  water  to  remain  in  the  state  of  water  it  needs  enough  energy  to  keep  its  molecules  moving  which  is  not  a  problem  in  our  lungs  where  it's  nice  and  warm.When  you  exhale  and  it's cold  outside  the  particles  of  the  water  vapour  begins  to  condense  into  lots  of  tiny  droplets  of  liquid  water  and  ice(solid  water).It  looks  like  a  cloud   in  the  air  and  looks  similar  to fog.When  it's  warm  out  things  are  different.When  we  exhale  and  it's  warm  outside  the  exahaled  air  gains  energy  and  thus  the  particles  remain  as  gas.The  invisible  gas thus  stays  invisible.