For the first order reaction, X→Y the time taken for 99.9% completion of the reaction is 500 minutes. Time taken for 75% completion of the reaction will be ------ minutes

t99.9%t50%=2.303K log 100100-99.92.303K log 100100-50; t99.9%t50%=3 log 10 0.3010; t99.9%t50%=10 ; t99.9%=10t50%; similarly t75%t50%=2.303K log 100100-752.303K log 100100-50; t75%t50%=2 log 2 log 2 t75%=2t50%; Conclusion :       t99.9%=10t50%;        t75%=2t50%;     t87.5%=3t50%;   t93.75%=4t50%; t 96.875%=5t50%;