how can i add questions and answers in a game?

to say more clearly,
for exampla i m developing a game.in game there will be question boxes and when you hit them there will come a question with 4 answers.true answer will give you something etc…

how and where can i store for example 50 questions with their answers and how can i call that questions at the best way?

Depends on your exact requirements…
If you want dynamic questions, you can load via web services.
if you want static 50 questions, you can store in a variable in script as a string, OR you can save in form of JSON to be more arranged.

firstly thanks for your answer. this will be for mobile. and i want to questions’ come randomly. not always the same question. for example i will use 20 question boxes and i will have 50 question to use. at every question there must be come 4 buttons to answer. i thought firstly playerprefs for use but did not not how to use it for this but now i will think on your recommendations. thanks again.

You could script a GUI and use GUI Skin to give it custom visuals.

The question could appear in a GUI Box
The answers could appear on GUI buttons so that they are clickable.