GCSE Science/Electricity multiple choice practice question 6

Image:Silver_plating_a_fork_(exam_Q).png A student decided to silver plate his/her mother's forks. S/he set up the apparatus above. S/he set the power pack and variable resistor so that the ammeter read 0.1 A. S/he allowed the fork to remain in the electrolysis apparatus for 10 min. Once s/he removed the fork s/he tested it by trying to scratch the silver off. S/he found that the layer of silver was too thin and decided that s/he would have to take steps to make the layer a lot thicker. Which one of the following steps would not produce a thicker layer of silver ? Increasing the voltage of the power pack Increasing the resistance of the variable resistance Increasing the time spent in the apparatus Increasing the concentration of the silver nitrate solution