Is it acceptable for an employer to make an interview and neglect the candidate by not giving him a refusal or acceptance answer in a given time ?

There are a number of scenarios in which you should or should not receive a reply.  The common practice is that if you are interviewed, then the interviewers should give you a rough time when they will contact you if successful or otherwise. If they don't, then you should ask!  The successful candidate should be contacted first because if they do not accept the position, then the next candidate can be offered the position.  If unsuccessful after interview then you should either receive a letter, an email or a telephone call within a few days of the final process.  There should always be an offer to feedback on the interview.  Even if successful, feedback can be useful for both the interviewer and the interviewee.

If you have applied then you should not expect a response.  Many adverts usually have a disclaimer saying "If you have not heard from us within x weeks/by x date, then assume that you have been unsuccessful on this occasion."  This eases the burden on having to email/write to/telephone potentially hundreds of candidates.

If there's a good hiring system, the employer shall send you a refusal letter mentioning the reasons of refusal. And in case of acceptance the employer shall send you an acceptance letter & this step should be preceded by sending the job offer which includes the job description, the package & hiring date.

It depends on the situation. As a HR professional we honor the candidates and respect their potentiality. When we call the candidate from that time we care to candidate. Who were attended in the interview and not performed better then we informed to send a regret letter. If interview in any lunch time then we arrange lunch for them.

yes an employer can change his/her decision at any time.

There are people who are better speakers than writers.And the reverse is also true.For those who are better writers than speakers, written questions to answer in writing may be beneficial since they'll better be able to express themselves.Using both methods can give a better picture of the candidate than just one.

Communicating refusal is not binding on employer. Selection is a complicated process and reason communicating can raise complications.

While it is not binding on the prospective employer to convey refusal, the candidate would have more respect in case a refusal is conveyed. Else a time frame should be given within which the candidate can expect a reply if he/she has been selected.

Nop.  its extremely rude to keep someone hanging without an answer.  just think if this happens to you how would you feel.  Plus it also stops that person from applying in other places or giving more interviews if you have given him or her any hopes because you did not have the courage enough to explain the reason of you not able to select them.  Every interviewee has the right to know why he or she was not found suitable.  so they can work on it.   I always inform the person in front of me as to why he is not yet ready for the job i have.  i also tell them how they can become suitable in the future so they can work on it.  And i find them actually leaving with a smile on their face.  WE ALL HAVE RESPONSIBILITY TOWARDS THE SOCIETY.  if we think something or someone can imporve, then do your best to get it done or arrange for it in whatever way you can.  i dont know if you guys agree with me but this is what i have ben practising and i feel good about it.  so do not keep someone hanging without an answer.  let them know what they can do to become suitable 

As good practice it should be answered back however answer should be encouaging to candidates.

However Practical not possible looking to have work load to recurites / HR, however can be made some automated system