A first order reaction is 75% completed in 100minutes. How long will it take for it's 87.5% completion? (a) 125 min (b) 150 min (c) 175 min (d) 200 min

After two half times 75% reaction is completed

Hence,

Half time = 50 minutes

After three half times 87.5% reaction is complete

Hence,

3 x 50 minutes = 150 minutes 

Therefore, for 87.5% completion of the first order reaction 150 minutes are consumed

So, the correct option is (b)