Think of Section 142 as the Assessing Officer's (AO's) investigation toolkit — the set of powers the AO uses before completing your assessment to gather information, scrutinise books, and if needed, call in an independent auditor. If Section 143(1) is a routine check, Section 142 is when the AO starts asking serious questions.
Section 142(1) — The Notice to Produce or File: The AO can issue a notice under 142(1) in two situations: (a) if you haven't filed a return — the AO can ask you to file one even after the due date; or (b) regardless of whether you've filed a return — the AO can ask you to produce books of accounts, documents, or furnish any information or statement in writing on any point. There is no time limit prescribed for issuing a 142(1) notice (unlike 143(2) which must be issued within 6 months). This is a favourite exam fact. Non-compliance is serious — the AO can proceed to make a best judgment assessment under Section 144, and you can face prosecution under Section 276D (imprisonment up to 1 year, or fine, or both).
Section 142(2A) — Special Audit (the powerful one!): This is asked in almost every attempt. If the AO believes your accounts are complex in nature — due to volume of transactions, specialised business, or doubts about correctness — the AO can, with the prior approval of the Principal Chief Commissioner or Chief Commissioner, direct you to get your accounts audited by a Chartered Accountant nominated by the Principal CIT/CIT. You cannot choose your own CA here. The cost of this special audit is borne by the Central Government (not you). The AO must give you a reasonable opportunity of being heard before issuing such a direction. The audit report must be furnished within the period specified in the notice (extendable by AO).
Section 142(3) — Opportunity of Being Heard: Before the AO uses any evidence or material collected during inquiry against you, they must give you a chance to explain. This is the natural justice principle embedded in the section. Don't ignore communications at this stage — anything used against you in assessment must first be put to you.