15. The half-life of the Sulphur-35 nucleus is 87.5 days. The decay constant for Sulphur-35 is (a) 9.2 x 10-8 s-1 (b) 1.1 x 10-8 g-1 (c) 3.4 x 10-8 s-1 (d) 2.7 x 10-8 s-1