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

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.