ANS:A - boundary mixer.

The most suitable equipment used to devulcanise rubber scrap and to make water dispersion & rubber solution is none of these. Here's a brief explanation of each option and why it might not be suitable:

1. Boundary Mixer:
   • Typically used for mixing highly viscous materials, but not specifically designed for devulcanising rubber or making water dispersions and rubber solutions.
2. Propeller Agitator:
   • Commonly used for mixing liquids or creating agitation in tanks but not suitable for the devulcanisation of rubber, which is a more complex process requiring specific equipment.
3. Sharpies Centrifuge:
   • Mainly used for separating components of a mixture based on density differences and not for devulcanising rubber or creating dispersions and solutions.

The most suitable equipment for devulcanising rubber scrap and creating water dispersion and rubber solutions would typically be a Banbury mixer or an internal mixer, which are specifically designed for processing rubber materials. However, since these are not listed as options, the correct choice among the provided options is none of these.