This question was fairly popular among the candidates. They performed fairly well in the (a) and (b) parts of the question but performed poorly in the (c) part of the question.
The factors responsible for instability in the prices of mineral products are:

• change in demand of consumers
• change in cost of minerals production
• availability of substitutes
• change in technology
• change in prices of substitutes e.g coal and oil
• government policies
• war, conflicts, etc