Dear Sakthi Sukumar,
When we read the text of any law, we should not lose sight of the arrangement of its structure. The text of every law is broadly divided into chapters , sections and schedules. Chapter is a main division of the Act whereas sections within the various chapters are minor divisions. Chapter heading denotes the particular aspects of the law dealt with in its various sections. Every chapter specifically covers certain aspects of the subject-matter of the Act and the aspects are detailed in seriatim through the various sections in the chapter. If you take the Industrial Disputes Act,1947 for instance it has been divided into seven chapters within which there are 40 sections on the whole.
Coming to the difficulty of interpretation of the notices of closure occurring in sections 25-FFA and 25-O expressed in your post, you should remember that sec.25-FFA pertains to chapter V-A whereas sec.25-O to chapter V-B. The heading of chapter V-A is " Lay-off and Retrenchment" whereas that of chapter V-B is " Special Provisions Relating to Lay-off, Retrenchment and Closure in certain Establishments". As per the opening section (25K) of chapter V-B, the provisions of this chapter applies only to those industries having not less than 100 workmen on their rolls.
Therefore, the notice period mentioned u/s 25-O is applicable to those industrial establishments falling under chapter VB only. The notice u/s 25FFA is, in short, applicable only in respect of establishments having 50 and above but below 100 workmen on rolls.