Which of the following materials is the least porous? loosely packed gravel sorted sand and rock unsorted sand and rock large pebbles and boulders

It is asked in this problem to determine which of the combination of materials is the least porous among all. Porosity is the ratio of the volume of pores or voids present per volume of the total mixture. Loosely packed gravel translaes to porous property already while big rocks can also employ large gaps in between. answer then is B.