If 75% of a first order reaction was completed in 90 minutes, 60% of the same reaction would be completed in approximately (in minutes) _______.

(Take : log 2 = 0.30; log 2.5 = 0.40)

A sample of milk splits after 60 min. at 300 K and after 40 min. at 400 K when the population of lactobacillus acidophilus in it doubles. The activa tion energy (in kJ/ mol) for this process is closest to__________.

(Given, R = 8.3 J mol^–1 K^–1, $$\ln \left( {{3 \over 2}} \right) = 0.4$$, e^–3 = 4.0)

During the nuclear explosion, one of the products is ⁹⁰Sr with half life of 6.93 years. If 1 $$\mu $$ g of ⁹⁰Sr was absorbed in the bones of newly born baby in placed of Ca, how much time, in years, is required to reduce much time, in year, is required to reduce it by 90% if it not lost metabolically.