The power to impose reasonable restrictions on free speech for the purpose of decency and morality (including obscenity) arises from:
\[\boxed{Article 19(2)}\] Article 19(1)(a) guarantees freedom of speech. Article 19(2) allows the State to impose reasonable restrictions on grounds of:
decency,
morality,
public order,
defamation,
security of the State,
contempt of court,
incitement to an offence, etc.
Obscenity laws, including those under IPC/BNS and the IT Act, derive constitutional legitimacy from 19(2).
Free speech under the Indian Constitution is not absolute, and the specific ground for restricting speech on the basis of decency and morality (which includes obscenity) is found by reading Article 19(1)(a) together with Article 19(2).
Article 19(1)(a) grants every citizen the fundamental right to freedom of speech and expression. This right is not unqualified. Article 19(2) permits the State to make a law imposing reasonable restrictions on the exercise of this right, and it lists the specific grounds on which such a law can be made. Decency and morality is one of the grounds named in the text of Article 19(2) itself, alongside public order, defamation, contempt of court, incitement to an offence, and the security of the State.
Because obscenity is treated in Indian law as an affront to public decency and morality, any statute that criminalises obscene content, whether printed, spoken, or transmitted electronically, draws its constitutional validity from this ground in Article 19(2). Without this ground, a law penalising obscene speech would fall foul of Article 19(1)(a) as an unreasonable restriction on free expression.
So when a statute such as the Bharatiya Nyaya Sanhita or the Information Technology Act criminalises obscene material, courts test that statute against the decency or morality ground of Article 19(2), not against public order or any other ground, since the harm being addressed is one of moral offence rather than breach of peace.
Therefore, the correct answer is Article 19(2).