mid term

Yes, that is correct - massive clay and single grain sand are both examples of structureless soils. And yes, massive clay only has micropores, and sand has only macropores.

Yes, macropores hold water more strongly than large (macro) pores. Consequently field capacity for clay would be higher than for sand.

Porosity (f) is defined as ratio of volume of all pores (Vf) relative to the total volume of soil (Vt). Hence, in a massive clay there will be a larger proportion of pore spaces (relative to total volume) than in the sandy soil.

For more explanation on this topic pls refer to your textbook