For a first order reaction, calculate the ratio between the time taken to complete three-fourth of  the reaction between the time taken to complete half of the reaction

The ratio constant for the first-order reaction is given by
 $k=\frac{2.303}{t}\log \frac{a}{a-x}$        
  Now, when three-fourth of the reaction is complete,
          
 and when the reaction is half completed, x = a/2
      
      Dividing (1) by (2), we get
       
Thus, the time taken for three-fourth of the reaction to be completed is double than that taken for half of the reaction