Which of the following impurity in cast iron promotes graphite nodule formation and increases the fluidity of the molten metal?

Answer: Option A

Silicon is an impurity in cast iron that promotes the formation of graphite nodules.

It also increases the fluidity of the molten metal, making it easier to cast.

Option B: Sulphur is incorrect because sulphur generally promotes the formation of iron sulfide, which is detrimental to the properties of cast iron.

Option C: Manganese is incorrect because manganese is used to counteract the effects of sulphur but does not promote graphite nodule formation.

Option D: Phosphorus is incorrect because while phosphorus can increase fluidity, it does not specifically promote graphite nodule formation like silicon does.


Conclusion:

Silicon in cast iron promotes graphite nodule formation and increases the fluidity of the molten metal.