Assessees required to File Return Of Income Compulsorily u/s 139(1)

Filing Returns Of Income is Mandatory/Compulsory If -

1. Companies and Firms (Whether having Profit Or Loss Or NIL Income).
2. Individual, HUF, AOP, BOI and Artificial Judicial persons. 
3. A Research Association, News Agency Or Trade Union Or Mutual Fund referred to in section 10(23D) Or Securitization Trust and Venture Capital Company/Venture Capital Fund.
4. A Person, being a resident Other than not Ordinarily resident, having Assets(Including any Financial Interest in any Entity), located outside India Or Signing authority in any account located outside India, Whether Or not having Income Chargeable to Tax.    

Note - If whose Total Income, Before giving effect of Chapter VI A or provisions of section 10(38), Exceed the Basic Exemption Limit. Applicable in above points(2,3 & 4).