after opening yes
they don't have to, but they keep longer if they do
Yes, if you want them to keep for more than a day.
Mold and other discusting things on your food if you dont keep refriderated and cooked.
No, mayonnaise is a condiment.
No, mayonnaise is not a gas. Mayonnaise is a semi-solid or thick liquid.
It depends on the mayonnaise. You can even get egg-free mayonnaise which is equivalent to an infinite amount of mayonnaise for each egg.
Mayonnaise is a noun.
Possibly...
mayonnaise
Usually they are about the same.
No. There are hair products that that use the word "mayonnaise" in them but it is not the mayonnaise you eat.
Mayonnaise and mayo are the same thing. "Mayo" is just a shortened version of "mayonnaise."