The executive was made almost entirely responsible to the provincial legislature by virtue of which Act during colonial times?

Government of India Act of 1935

As the demand for representation grew, the British had been forced to introduce a series of
constitutional reforms. A number of Acts were passed (1909, 1919 and 1935), gradually enlarging the space for Indian participation in provincial governments. The executive was made partly responsible to the provincial legislature in 1919, and almost entirely so under the Government of India Act of 1935.