One way to extract metals from land contaminated with metal compounds is phytoextraction. When plants grow they absorb metal ions through their roots. The plants are harvested, dried and burned

forming an ash. The ash contains metal compounds. Plants were grown in a piece of ground contaminated with nickel compounds. (i) 1 kg of the ash from these plants contained 142.0 g of nickel compounds. Čalculate the percentage by mass of nickel compounds in the ash. (ii) Nickel is extracted from nickel compounds. Štate an advantage of extracting nickel by phytoextraction rather than from its ore.