Which of the following incident led to the signing of the instrument of accession by Raja Hari Singh of Kashmir after the independence of India?

Attack on Kashmir by Pakistan's tribal infiltrators.

In October 1947, Pakistan sent tribal infiltrators from its side to capture Kashmir. This forced the Maharaja to ask for Indian military help. India extended the military support and drove back but only after the Maharaja had signed an ‘Instrument of Accession’ with the Government of India.