Question

the main purpose of a boiling water is to convert cold ocean water into steam. spin a large metal turbine. generate electricity for our society. recycle used ocean water.

Explanation:

A boiling - water reactor ultimately aims to generate electricity for society. Converting cold ocean water into steam and spinning a large metal turbine are intermediate steps in the electricity - generation process. Recycling used ocean water is not the main purpose.

Answer:

generate electricity for our society.