The correct option is (d) All of the mentioned
To explain: Catalytic reductions can be carried out in batches or in continuous processes, in the liquid phase or in the vapour phase. This method has many advantages over other methods of reduction, particularly for large-volume production. With low-cost hydrogen, as is the case when by-product hydrogen is available from other installations or when large hydrocarbon steam units are installed, this process cannot be matched by other methods of reduction in so far as economics and quality of product arc concerned.