The Princely State whose territories were merged into India after a ‘Plebiscite’ was :
(1) Kashmir
(2) Manipur
(3) Junagadh
(4) Hyderabad

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A plebiscite was held on 20 February 1948 in Junagadh and most of Junagadh's population voted to join India, after which it became a part of India.
The Government of India accepted the accession of Junagadh & Junagadh officially became a part of India on February 20, 1948.