A constitution is a set of fundamental principles or established precedents according to which a state or other organization is governed. These rules together make up, i.e. constitute, what the entity is. When these principles are written down into a single or set of legal documents, those documents may be said to comprise a written constitution.

Act: A bill which has passed through the various legislative steps required for it and which has become law. Act is a law according to broad guidelines given by the constitution.

The Government of India Act 1935 was an act not a constitution because India was not an independent country and governed by British as a subject and that was enacted by the British Parliament and hence Government of India Act 1935 was a part of British law or constitution.

According to my knowledge no act was enacted in 1948.

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“There is no God but You (Allah Almighty), You are far exalted and above all weaknesses, and I was indeed the wrongdoer”. AL-QURAN