Correct Answer - C
Time required for the conversion of 0.8 mol of A into 0. 6mol of `B=(0.6)/(0.8)=0.75rArrt_(75%)`
Similarly, the time required for the conversion of 0.9 mol of A to 0.675 mol of B is `(0.675)/(0.9)=0.75rArrt_(75%)`
Hence, both cases requires 1 h.