Assuming no change in volume, the time required to obtain solution of pH =4 by electrolysis of 100 ~mL of 0.1 M NaOH (using current 0.5 ~A ) will be

Step-by-step solution

[ H ⁺ ]=10⁻⁴ M No. of moles of NaOH in 100 ~mL solution = M V 1000 = 10⁻⁴ 100 1000 =10⁻⁵ Mass of NaOH in solution =10⁻⁵ 40=4 10⁻⁴ ~g By Faraday's law, W= I t E 96500 aligned or 4 10⁻⁴ & = 0.5 t 40 96500 t & = 4 10⁻⁴ 96500 0.5 40 =1.93 ~s aligned