Who should be the official spokesman for the organization; Leader,Particular person or the Owner and on what this function depend ?

Thanks for invitation.  

As a standard practice, Chief Communication Officer or Public Relations Officer is the official spokesperson of the organization. However, in highly important strategic issues, The Chief Executive Officer/ Managing Director (Leader) takes the role of spokesperson and briefs the issues to the public/govt./and other stakeholders

It depends upon the size of the organisation. However, When there is a need of Spokes-Person, the organisation certainly will have one and until such time, the responsible person like the owner will have to take care.

some companies have public relation section the manager of this section can be the official spokesman of the organization

You did mention it in your statement; "spokesperson". It is wrong, unethical & unprofessional for the owner to speak on behalf of the organisation unless they are called upon to do so especialy in times of emergeny or where it necessitates to do so. An organisation is meant to have a professional spokesperson who has got prior knowledge, experience & qualification in Public Relations; in other words a Public Relations Officer, Executive or Manager

I think CEO is the best one who can take this role because he knows more than anyone about what and when to say anything about the organization

agree with the both experts.........

You are referring to a smaller company, which will not have a PR department.

In very small businesses, the spokesperson should be the owner/entrepreneur.  Nobody else will be taken seriously.

In businesses of any size, the spokesperson should be selected primarily on their ability to speak in public.   In general it should not be the owner or CEO, although it is very important that they have direct access to the owner/CEO.    The CEO has other things to do, and should only appear in public like this in the most important of circumstances.

Agree on experts answers. Thanks for your invitation.