how does sex takes place.................................................................................

This question must not be asked in this way. Is there any question like this asked in entrance exams.

First of all considering this as a wrong or irrevelant question is not right. Sex is a natural process and considering it as  something wrong or odd is just one of those wrong things which are stopping us in the list of some underdeveloping countries.

Now coming to your question: How sex takes place? The answer is simple. It is a result of physical interaction between male and female with their body reproductive parts which they do to get pleasure and also a child which is necessary for continuation of life