Section 23(1)(b) in THE DELHI INDUSTRIAL DEVELOPMENT, OPERATION AND MAINTENANCE ACT, 2010
(b)where the person to be served is a firm, if the document is addressed to the firm at its principal place of business, identifying it by the name or style under which its business is carried on, and is eitherÂ(i)sent under a certificate of posting or by registered post; or(ii)left at the said place of business;